“I hate the 'Time Warp'!” says Simon Pegg's character Tim Bisley in the sitcom Spaced, in a speech that's surely as familiar to Rocky Horror haters as any of the show's audience participation callbacks are to its devotees. Altogether now: “I don't care! I hate it! It's boil-in-the-bag perversion for sexually repressed accountants and first-year drama students with too many posters of Betty Blue, The Blues Brothers, Big Blue and Blue Velvet on their blue bloody walls!” There's every likelihood that Bisley is channelling the views of Pegg himself, as the star was also co-writer of the show. And I know exactly where Bisley/Pegg is coming from.

I have no personal axe to grind, here. I've met precisely two minor members of the cast, and I didn't mention Rocky Horror to either of them. When Christopher Biggins – who I mainly remembered not as a Time Warping Transylvanian but as a dreadful guffawing Tory from the TVam sofa – proffered his hand to be shook at some launch party or other, I drunkenly told him I was “just relieved to see it isn't a claw”. When I had a five-minute meet and greet with Meat Loaf, I went on about 'You Took The Words Right Out Of My Mouth' rather than a cinematic cameo that was, let's face it, hardly the highest point of his career.

My animus is, or at least was initially, directed towards the subculture surrounding the film. My first encounter with Rocky Horror was, as Pegg accurately pinpoints, as a first-year student. In the late 80s, university Rocky Horror parties seemed to alternate with Blues Brothers ones as the single most common form of undergraduate social activity. My best mate Tony, who lived across the corridor from me, had thick curly black hair, heavy-lidded eyes and full lips, and made the most of his uncanny resemblance to Tim Curry by turning up to such events in full Frank-N-Furter regalia (and, in the circumstances, who can blame him?).

For me, though, the equation of men in Ann Summers lingerie with sexual perversion was too on-the-nose and tacky. It gave the squares permission to be temporarily un-square in a socially-acceptable context, in much the same way that Hallowe'en turns everyone into a goth once a year.

I also disliked the codified call-and-response routine which had grown up around the show. Like knowing when to shout out that the narrator Charles Gray “has no fucking neck”, when to throw rice, or rattle a newspaper, or spray water around. There was something strangely joyless about the ritual, like reciting prayers at school. Furthermore, the supposed spontaneity of the audience interaction was undermined by the act of learning by rote and repeating the witticisms of other, nameless Rocky Horror fans from a decade-plus earlier, much in the same way that reciting the Parrot Sketch from Monty Python is an unfailing trademark of the tedious wit-vacuum.

As the years have passed, however, I've learned to love Rocky Horror, despite all those misgivings. There are many reasons for this, but one is that the film, and the stage show which preceded it, are closely connected to at least one, arguably two pop-cultural movements I hold dear: glam and punk. Indeed, the show's central mantra “DON'T DREAM IT, BE IT” taps into the heart of both: the self-transformation inherent to glam, and the D.I.Y. anyone-can-do-it ethos of punk.

There are those, like Barney Hoskyns, author of Glam!, who see Rocky Horror as a “co-opting”, an opportunistic cash-in on glam's popularity. I respectfully disagree. In hindsight, it appears truer, if anything, to argue that Rocky Horror was integral to glam. It's a misreading of that movement to see it in such linear terms. It's not as if David Bowie threw on a dress one day, and everyone else spent the entire early Seventies desperately chasing his bandwagon. Some ideas, like toying around with gender, were just in the air. For example, Andrew Logan was launching his Alternative Miss World around the same time. Meanwhile, across the Atlantic, John Waters was pioneering shock-filled trash cinema with the transvestite (but not exactly sweet) Divine.

Furthermore, the Rocky Horror ensemble mingled with their musical counterparts. Little Nell, who played Columbia, had a stall at Kensington Market next to Freddie Mercury's. Mick Rock, court photographer to glam royalty, took the classic portrait shots of the cast. The make-up for the film version was created by Pierre Laroche, who designed several classic Bowie faces, including the gold forehead disc and the Aladdin Sane lightning bolt. The Rolling Stones began using their iconic mouth trademark after Rocky Horror's lips-and-teeth logo (itself inspired by Man Ray's 1936 Surrealist painting 'Observatory Time: The Lovers'), not before it.

And to the extent that Rocky Horror was a tribute to/parody of sci-fi B-movies, as opposed to a sex romp, it chimed with glam's fascination with classic cinema (think Bowie's 'Drive-In Saturday', Roxy's 'Virginia Plain', Sparks' 'This Town Ain't Big Enough For Both Of Us'). Rocky Horror was part of that cultural current, not a cynical adjunct to it. In his book Performing Glam, Philip Auslander wrote “At one level, the association of Glam with gothic horror, particularly the Hollywood films of the 1930s satirized by The Rocky Horror [Picture] Show that popularized the nineteenth-century novels on which they were based, makes perfect sense. As Harry M. Benshoff has shown in Monsters In The Closet, those films, many of them directed by the avowedly gay James Whale, contain multiple, coded references to homosexuality and reflect a covert queer sensibility based on an identification of the queer and the monster as the Other.”

The connection with punk may seem more flimsy, at first glance. Some of the links are purely social: in December 1973, West One magazine selected Little Nell and Vivienne Westwood as 'London Belles' with the city's strongest style for a photo shoot. Later, Nell briefly dated Adam Ant, another tenuous connection between Rocky Horror world and the Kings Road punk rock set. It seems inconceivable, however, that Westwood and her partner Malcolm McLaren would have been unaware of a musical featuring fetish wear taking place on Kings Road, a stone's throw from their clothes shop, when they took the decision to switch from selling Teddy Boy threads (trading as Let It Rock) to bondage gear (as Sex). Rocky Horror star Patricia Quinn is absolutely certain of the show's influence: “I maintain that Sue Blane (Rocky Horror costume designer) invented punk,” she argued on the audio commentary for the film's 25th anniversary DVD, perhaps overstating the case slightly. “And this show invented punk. And down the road was Vivienne Westwood with her shop Sex. And she thinks she started punk, but she just copied us, down the road.” Richard O'Brien, the show's creator, can be heard to agree (if only to humour her).

Another thing that was in the air in 1973 was a rock & roll revival. This premature hankering for the era of the jukebox and bobby-socks arguably began in 1969 with doo-wop troupe Sha-Na-Na (contributors, later, to the Grease soundtrack), who performed as the penultimate act at Woodstock, early on the Monday morning, to a crowd of 200,000 frazzled hippies grateful for the comfort of some melodicism and familiarity. But, in his book Retromania, Simon Reynolds pinpoints 1973 as the year it peaked, citing films like American Graffiti and That'll Be The Day, the London opening of the musical Grease, songs like 10cc's 'Rubber Bullets', Elton John's 'Your Sister Can't Twist (But She Can Rock'N'Roll)' and John Lennon's Rock'N'Roll album (recorded in '73 but held back for release until '75). One could also add pop groups such as Mud (glam rock Teddy boys, essentially) who began having hits in 1973, Showaddywaddy who formed that year, even the ooh-wahs of Bowie's aforementioned 'Drive-In Saturday', plus, of course, McLaren and Westwood's also-aforementioned Let It Rock boutique. And The Rocky Horror Show. That Fifties-sounding soundtrack wasn't a bolted-on afterthought, but central to the concept from the start: when Tim Curry auditioned for the lead role, he sang 'Tutti Frutti' by Little Richard.

The final element was the growing respectability, or at least acceptability, of overtly sexual themes in film. Sexploitation cinema had been pioneered in the States in the 1960s by the trashy, tits-obsessed (but hugely enjoyable) 'Mondo' movies of Russ Meyer, and perhaps uncoincidentally, there's a definite flavour of Frank-N-Furter to the character of Ronnie 'Z-Man' Barzell, the male protagonist of Meyer's most mainstream work, Beyond The Valley Of The Dolls (1970). In France, the films of Jean Rollin combined sex, horror, surrealism and art, most notably on Le Frisson Des Vampires (1970). At the same time, the UK saw a boom in sex comedies like School For Sex (1969) and No Sex Please, We're British (1972), followed by the hugely popular Confessions series, all starring Robin Askwith, which ran from 1974 to 1977. The groundbreaking American crossover-porn movie Deep Throat was released in 1972, the same year as Bernardo Bertolucci's then-shocking Last Tango In Paris. Soft-porn blockbuster Emmanuelle followed in 1974. Meanwhile, the growth of underground exploitation cinema continued. Ilsa, She-Wolf Of The SS came out in 1975, the same year as The Rocky Horror Picture Show, as did the film adaptation of The Story Of O. Tinto Brass' Salon Kitty and Caligula were just around the corner. Orgiastic, exploitative, transgressive films were coming out of the XXX joints of Soho and into the local picture house, and were already enough of a fixture in the public consciousness to be a successfully parody-able genre.

It was by being in the right place at the right time to catch all four of these waves - B-Movie nostalgia, gender fluidity, rock'n'roll revivalism, sexualised cinema – that Richard O'Brien, a jobbing actor who grew up in New Zealand but was now in and out of work in London, functioned as a human aerial, channelling them into the Rocky Horror project.

On and off, during downtime, 31-year-old O'Brien had been writing a musical about schlocky B-movies in his flat in Maida Vale and, with the help of theatrical director Jim Sharman, who had previously cast O'Brien in Hair and Jesus Christ Superstar, he began to knock it into shape, firstly under the title They Came From Denton High, and subsequently The Rocky Horror Show, with the help of composer Richard Hartley. After a series of chance meetings, O'Brien reconnected with Tim Curry, who had also appeared in Hair. The Rocky Horror Show had a writer, a director, a script, and a star.

Curry's Frank-N-Furter wasn't always the dark-haired apparition with the cut-glass diction that we know and love. At first his locks were dyed peroxide blond, and he experimented with German and American accents before settling upon the voice of what Sharman described as a “Belgravia hostess-with-the-mostest”, after Curry had overheard one Sloane Ranger asking another whether they owned “a hice in the tine, or a hice in the country”.

The cast, too, wasn't identical to that which became immortalised by the film. Along with Curry, it comprised future Evita star Julie Covington as Janet, RSC and Royal Court regular Christopher Malcolm as Brad, Belfast-born Patricia Quinn as Magenta and The Usherette, the aforementioned Australian actress Little Nell (nee Nell Campbell) as Columbia, stage veteran Jonathan Adams as The Criminologist/Narrator, Paddy O'Hagan as Eddie and Dr Everett V Scott, O'Brien himself as Riff Raff, and Rayner Bourton as the titular Rocky.

Bourton, for one, was not immediately convinced. He considered the script “tacky”, and feared he would be arrested for taking part in what he described, in his autobiography, as “soft porn”. (Far worse happened to him, but we'll come to that.) His fears weren't entirely fanciful. Or at least, they wouldn't have been, just five years earlier. The Theatres Act of 1968, which ended centuries of governmental censorship of plays, made male nudity on a stage a possibility, directly enabling productions such as Hair, which opened in the West End in September 1968 (indeed, its opening was specifically delayed until the Act had passed). Broadcaster Danny Baker frequently tells the traumatic tale of the occasion he attended Hair as a teenager, sat in an aisle seat, and a dancer's dangling member brushed against his ear.

The Theatres Act, while removing the requirement for licensing by the Lord Chamberlain, did lay down a definitions of prosecutable obscenity as any performance which was likely to “deprave and corrupt” those who attended it (leaving the get-out clause that the play could be “justified as being for the public good on the ground that it was in the interests of drama, opera, ballet or any other art, or of literature or learning” in the opinion of experts in the field, which would provide lawyers with plenty of employment for years to come). Given that Rocky Horror's entire raison d'etre was to deprave and corrupt, the show was indeed playing with fire.

The past is another country, and as vanilla, softcore and on-the-nose as the show may seem to modern sensibilities, the Britain of 1973 was in the grip of a growing illiberal backlash against the freedoms of the 1960s, led by the Christian reactionary Mary Whitehouse and her National Viewers And Listeners Association. After the liberal gains of the Harold Wilson era, which had seen the relaxing of abortion laws and the decriminalisation of homosexuality (in addition to the Theatres Act), the socially-conservative Edward Heath was now Prime Minister. The whole country, after a jump to the Left, was taking a step to the Right.

After a preview show three days earlier, The Rocky Horror Show opened on Tuesday 19 June 1973 at the Royal Court's 63-seat Theatre Upstairs on Sloane Square, describing itself as “a mysterious web of mad mutants, tame transvestites and muscle-bound monsters”, its crude, hand-drawn programme promising “something for everyone”. Entry was 50 pence (students half-price), though it later shot up to 80p. The tiny room's tin roof meant that performances had to be cancelled whenever it rained, because the noise drowned out the dialogue.

Real-life horror B-movie legend Vincent Price, whose wife was in a production downstairs, was in attendance that first night. Perhaps more significantly, Jonathan King, lured in by a positive review from the Mail's Jack Tinker, saw the second night, and promptly became one of the show's financial backers (along with impresario Michael White), signing the cast up to his UK Records label to rush-release the soundtrack album. It was recorded on the first weekend, at Jill Sinclair's Sarm East studios on Brick Lane, but without Julie Covington, who had suffered an accident was replaced by Belinda Sinclair. The session was completed at a knockdown price because, according to King, Sinclair wanted a “big name” for her studio's CV. As he puts it in his autobiography with typical self-effacement, “I was, at the time, the hottest record producer in Britain, possibly the world.”

The show was a late-night performance, beginning at 10.30pm, a relative rarity at the time which had the dual effect of attracting a drinking crowd and ensuring a cult following of people who might not normally attend the theatre. Its first run continued for just one month, and the final performance on 20 July 1973 – with Mick Jagger and Omar Sharif waiting in the audience – had to be cancelled for a reason which was kept secret at the time, but is now one of the most famous Rocky Horror anecdotes of all: Rayner Bourton, playing Rocky, couldn't go onstage because some glitter from his gold hotpants had worked its way under his foreskin, inflaming his penis to the size of a watermelon, meaning that he could no longer fit inside his costume.

The show reopened on 14 August at the 230-seater Chelsea Classic Cinema a few blocks away on Kings Road and ran till 20 October, by which time it had received glowing reviews in The Guardian, Financial Times and Punch, where none other than Barry Humphries wrote “It would be impossible to overpraise The Rocky Horror Show, which has now settled into the Chelsea Classic Cinema as snugly as an evil spirit into a Gadarene swine”, adding “Rocky Horror is a lewd and loveable show, reeking with grime, gunpowder and gusset, and laughter flows with haemophiliac abundance”. At the Evening Standard Theatre Awards, it received the gong for Best New Musical.

On 3 November the show finally found a long-term home, the 350-seat Kings Road Theatre at 279 Kings Road, which in a previous life had also been a cinema called the Essoldo, and earlier still, a pioneering ice rink called The Glacarium (it's now a Cineworld), where it stayed for six years, before moving for one last year to the Comedy Theatre on Leicester Square where it eventually closed on 13 September 1980 after a total of 2960 performances.

The show's transfer to America had mixed fortunes. The US rights were snapped up by legendary music mogul Lou Adler, who put it on at his own Roxy Theater in Los Angeles from 24 March 1974 (Jonathan King, annoyed at the rights being poached from under his nose, flooded the US market with import copies of the UK soundtrack, and placed billboards for it opposite the Roxy). The LA production featured a handful of transplants from the London cast including Curry and O'Brien (the backroom staff included the future Senator Al Franken, working as a lighting technician). It was a hip show to be seen to attend: Elvis Presley and Raquel Welch were among those who went, as was Keith Moon who, as Meat Loaf told VH-1 in an interview, would line up bottles of champagne on the stage for each of the cast, and Carole King, who had actually started dressing as Magenta by the end of the residency. It was during its nine-month run in Hollywood that the film deal was struck with 20th Century Fox.

The Broadway run wasn't such a success, opening at the Belasco Theatre on 10 March 1975 to a mauling from the critics. Tim Curry was obliged to appear on the Today Show the next day where, humiliatingly, the reviews were read out to him. (That said, two of the choice descriptions of Curry himself, “a mixture of Joan Crawford and Burt Lancaster” and “Mick Jagger, David Bowie and Marc Bolan all in one”, are hardly insulting ones.) Less than a month later, after just 45 performances, the Broadway version closed, but it didn't matter because film-wise, the ball was already rolling. Fox's incoming Creative Director Alan Ladd Jr was known not to be keen on the project he'd inherited, which may have had implications for the show's low budget. With some reluctance, Rocky Horror got the corporate nod.

Filming began at the old Hammer lot at Bray in Berkshire, with the main location being nearby Oakley Court, a Victorian Gothic mansion previously owned by 19th century politicians and grandees, and used in countless Hammer Horror productions. At the time the Rocky Horror Picture Show was made, it was in a state of considerable disrepair and dilapidation, with lead missing from the roof and completely absent floorboards. (It's since been renovated as a posh hotel, in whose grounds Rocky Horror fans hold an annual picnic.)

Jim Sharman was retained from the stage show for the job of directing his first major film, as was set designer and fellow Aussie, Brian Thomson. The cast, too, was largely the same as the London line-up, with a handful of significant alterations. Californian actor Barry Bostwick, previously a Tony award winner for playing Danny Zuko in the Broadway production of Grease, and the then little-known Susan Sarandon, whose superb performance as the simpering, swooning Janet was assisted by the fact that she was genuinely suffering from flu throughout. Rising rock & roller Meat Loaf was brought over from the Broadway cast to play Eddie, his audition so enthusiastic that it resulted in a broken chandelier. (However, the first time he witnessed 'Sweet Transvestite' in rehearsals, he was so shocked that he walked out, and had to be persuaded not to quit.) Peter Hinwood, a musclebound model, was cast as Rocky, and Jonathan Adams was shuffled over to the role of Dr Scott to make way for Charles Gray, best known as Bond nemesis Blofeld, as the criminologist.

The presence and personality of the show's creator, however, was indelibly printed across every frame. Indeed, the first thing we see is a pair of disembodied lips, belonging to Patricia Quinn, heavily rouged and hanging suspended in blackness. They're lip-synching to the voice of O'Brien himself, singing the film's opening number, 'Science Fiction/Double Feature', a sentimental 1950s-style ballad which sets down several markers for the film's universe by listing a litany of three-quarters-forgotten B-movie actors (Jeanette Scott, George Powell, Anne Francis) and the films (When Worlds Collide, Forbidden Planet) in which they starred. Rocky Horror's affection for its source genre could not be clearer.

The first scene, however, begins in classic B-movie style by depicting a world of wholesome normality, just waiting to be disrupted. We find ourselves in the fictional and proverbially WASP-y town of Denton, Ohio, which proclaims itself 'The Home Of Happiness' on a welcoming billboard, where straight-laced courting couple Brad Majors and Janet Weiss are attending the wedding of their friends Ralph Hapschatt and Betty Munroe.

The only minuscule hint of unease, at this stage, is provided by what's hanging on the church wall: Grant Wood's famous 1930 painting 'American Gothic', depicting two puritanical farming folk stood in front of a wooden house holding a pitchfork, echoed subtly by the lurking figures of Quinn and O'Brien, at this point mere background extras. Janet catches the bride's bouquet, a traditional omen that she'll be the next of the gang to marry, which inspires Brad to break away from the congregation (whose number includes future soft-porn actress and Prince Andrew love interest Koo Stark) in order to propose via the medium of song: the exuberant duet 'Dammit Janet'.

We cut to the narrator, a criminologist in a dimly-lit study, giving a to-camera introduction to the tale, explaining that the newly-engaged couple were heading off by car to visit their friend, and former tutor, Dr Everett Scott. We cut back to Brad and Janet, now driving through the woods at night, while President Nixon's resignation is unfolding on the radio (a detail O'Brien disliked, as it pins Rocky Horror to a specific era), and Hell's Angels whizz past recklessly on motorbikes. Suddenly, a tyre has a blowout, whereupon Brad and Janet ignore the first rule of horror: if you break down in the woods, don't get out of the fucking car. They both do.

Huddled under a newspaper, failing to heed a hand-painted Enter At Your Own Risk sign, they walk down the driveway of an ominous gothic mansion, singing another song, 'There's A Light (Over At The Frankenstein Place)' which honours Rocky Horror's influences. At the house's creaking wooden door, they're greeted by a hunchbacked butler, the resentful Riff-Raff, played by O'Brien, who ushers them into a stereotypically spooky hallway (cobwebs, taxidermy, a grandfather clock with a skeleton inside, that 'American Gothic' painting again), where we properly meet Patricia Quinn in the role of her life as the maid, Magenta. Her corkscrew curls sprayed red for the part, the Northern Irish actress slides down the banister, and hams it up like her life depends on it, gleefully cackling “You're lucky, he's lucky, I'm lucky, we're all lucky!”

Brad and Janet, still holding out for someone to let them use the phone to call for a breakdown service, are led into a ballroom where dozens of garishly-clad revellers, the same people who zoomed past on motorbikes - not Hell's Angels, we shall learn, but 'Transylvanians' - are having some sort of a party. Cue the song. THAT song. 'The Time Warp', with its hands-on-hips and pelvic thrusts, is a straight-up parody of the dance-craze records of the early Sixties, and yes, it is bloody annoying when you've heard it for the billionth time. (It has to be said that whatever you think of the song, the romping rock & roll soundtrack in general - produced by Richard Hartley at Olympic Studios with a band of session men led by sometime Free and The Who member John 'Rabbit' Bundrick and featuring two members of Procol Harum – is an absolute joy.)

In the film, Simon Pegg's worst musical nightmare serves as our introduction to the helium-voiced, top-hatted Columbia, played by 'Little Nell' Campbell, an Australian former busker, housekeeper and, crucially for this role, tap-dancer. Aside from Rocky Horror, she is arguably best known for a TV performance of her single 'Do The Swim' in which she repeatedly (and, supposedly, accidentally) exposed her breasts, shown endlessly on Denis Norden's bloopers show It'll Be Alright On The Night. The song 'Laura' by Bat For Lashes is dedicated to Campbell and her unquenchable joie-de-vivre, and based purely on her performance in Rocky Horror, it's easy to understand why.

And now, Enter The Drag 'Un. The arrival of Frank-N-Furter in The Rocky Horror Picture Show is, quite simply, one of the greatest entrances in cinematic history. The first glimpse we get is a pair of stack-heeled shoes, as he is filmed with his back to the camera in a descending cage lift, his modesty protected by a silver-collared black velvet cape. Tim Curry turns, and turns in a real bravura performance, blood-red lips glistening, eyes flashing, strutting like a satyr, then the big reveal as the cape drops (and, very nearly, so does Janet). In his fishnets and corset, the Lord and Lady of the Manor romps through 'Sweet Transvestite', his burlesque-glam signature tune making false promises about a “satanic mechanic”, dropping hints about his forthcoming Frankenstein shenanigans, and breaking the fourth wall with an exquisite expression on the line “You look like you're both pretty groovy...” If the film had given us nothing else – if Tim Curry's CAREER had given us nothing else – it would still have been worth it just for those four minutes. Wow.

One fascinating possible source of Frank's character, based on this first sighting, has been proposed by Roger Baker who, in his 1995 book Drag: A History Of Female Impersonation In The Performing Arts, sees echoes of a Greta Garbo character. “Perhaps Garbo's greatest screen role, Queen Christina, a seventeenth century Swedish monarch with a penchant for wearing male attire and almost certainly a lesbian, allowed the star to fully exploit her own ambiguity. Interestingly, Garbo's appearance in this film is echoed by Tim Curry as Frank-N-Furter in The Rocky Horror Picture Show.”

Within seconds of the charismatic master's arrival, the new houseguests are stripped down to their underwear by Columbia and Magenta, and taken to a Greco-Roman atrium where Frank, now in green medical scrubs bearing a pink triangle (a Holocaust reference which may hint that his character's human experimentation is as much inspired by Joseph Mengele as by Dr Frankenstein), a reginal string of pearls and pink marigolds – an ensemble which is, if anything, more unsettling than the black basque – prepares to give life to the lifeless, in more senses than one. Brad, for now, maintains his decorum, but Janet is clearly in Frank's thrall.

Then it all gets REALLY silly. A bandaged body in a briny tank is zapped into life, and Rocky – a buff Boris Johnson in gold hotpants – is unwrapped. The songs ('Sword Of Damocles', 'I Could Make You A Man') ensue, and Furter drools over his lab-made sex toy, with ravenously camp desire: “Oh! Rocky...”

Now it's the turn of Eddie/Meat Loaf, a greaser with half his brain missing (the other half having been used in the making of Rocky), busting out of a freezer on a Harley Davidson, in a scene which resulted in serious leg injury for Meat Loaf's stunt double (and a head wound for the Loaf himself). As he belts out rock & roll number 'Hot Patootie', we see Janet joining in (to a disapproving glance from Brad), before Frank finishes him off with a pick-axe. Disruption over, Frank and Rocky are 'married' in a wedding chapel.

What follows are probably the most problematic few minutes of the film. Brad and Janet are obliged to stay the night, and in a sequence of shadowplay sex scenes (watched on CCTV by Riff Raff and Magenta), the predatory lothario Frank visits the bedchamber of each guest in turn, pretending to be their fiance(e), and seduces them. They're both shown to be enjoying the sex, even after their visitor's true identity has been revealed, as though they've fallen prey to a form of sexual Stockholm Syndrome. It is, at the very least, rapey, and if we're going to be honest about it, actual rape, but it's played like the whole thing's a jolly hoot. (Richard Curtis' 2009 film The Boat That Rocked was rightly criticised for a similar gag, but in Rocky Horror it passed without comment. The Seventies truly were, as stated earlier, another country.)

Another taboo topic the film touches upon, less explicitly, is that of incest. It's implied that Riff-Raff and Magenta are brother and sister, and the odd glance here and gesture there suggests that there's a subtext to their relationship that goes beyond sibling affection. During a scene in which they torment a bewildered Rocky with candles after he's broken loose, the two servants share what Quinn and O'Brien describe on the DVD commentary as “an elbow-fuck”.

The farcical twists begin to flow thick and fast. With Columbia and Magenta watching on CCTV, Janet has a tender tryst with Rocky, while singing 'Touch-A Touch-A Touch Me'. Meanwhile, Frank punishes Riff Raff with a whip, adding to the butler's simmering grievances against his Lord. A visitor arrives, and it's Brad and Janet's old teacher Dr Scott or, as we'll discover, Dr VON Scott. There's an awkward banquet scene during which the Transylvanians appear confused about the function of cutlery, providing the strongest hint yet that Transylvania is an alien galaxy rather than a region of Europe, and Transsexual is Frank's home planet rather than just his gender identity.

Via the song 'Eddie's Teddy', we learn that Dr (Von) Scott is Eddie's uncle who is searching for his missing nephew, and may also be investigating UFO activity. In another subtle reference to classic cinema, Columbia sings a line while lying in the actual crib Fifties comedy Baby Doll. To Brad and Janet's horror, the sight of a half-eaten Meat Loaf under a glass tabletop alerts them to the fact that they've been dining on Eddie in more senses than one. The actors' shock was real: apart from Curry, Sharman hadn't warned any of them that Meat Loaf was lying there.

As Frank mocks his appalled guests with the taunting 'Planet Schmanet Janet' (refrain: “You better wise up Janet Weiss”), they try to make a run for it, but are trapped, and Furter turns Janet, Dr Scott, Brad, Rocky and Columbia into statues with his Medusa Transducer, then re-animates them – dressed as him - for a floorshow, singing 'Rose Tint My World'. Frank descends to sing 'Don't Dream It, Be It', and magically ends up in a swimming pool with Michelangelo's David at the bottom (a reference to Frank's hubristic attempts at playing God) while singing 'Wild And Untamed Thing'. The others jump in for an orgiastic scene which includes the briefest of lesbian kisses.

Frank's downfall comes when Riff Raff and Magenta enter the theatre in new sci-fi alien guises, the former with a ray gun which echoes the American Gothic pitchfork, the latter with Bride Of Frankenstein hair. Knowing the game's up, Frank sings the valedictory ballad 'I'm Going Home'. Columbia, still loyal, leaps in front of the death ray to save him, and is killed. It only delays his inevitable fate: Frank gets zapped. In a blatant homage to King Kong, Rocky carries his owner's corpse and climbs the RKO mast on the stage backdrop, but he too is mercilessly zapped, and they both fall dead into the swimming pool in a scene reminiscent of the opening - and closing - scene of Sunset Boulevard. And an external view shows the entire house – which we now learn was a spacecraft all along – getting beamed up.

And that's your lot, depending on which version you're watching (some cuts have a battle-scarred Brad crawling through wreckage and singing 'Superheroes', excised from the theatrical release). In the space of a couple of hours, in a scattershot and scant way, it's a film which deals with, or touches upon, homosexuality, transvestitism, cannibalism, aliens, nazis, voyeurism, workers' insurrection, incest, murder and reanimation. It's far from perfect: for one thing, the pacing's off, and it blows its biggest songs in the first fifteen minutes. As Richard Hartley told The Guardian earlier this year, “I'm staggered it's such a phenomenon. The film's a bit long, and it's so slow. It wilts after an hour then picks up again.” But it's also far from the milky-mild kink-sploitation pic its haters would have you believe. When Jim Sharman said, in a behind-the-scenes interview on set, that “I would like it to get a U certificate, I suppose, like a 1970s version of The Wizard Of Oz”, his tongue was firmly in cheek.

The film, though not a runaway success on its initial release in 1975, became by some reckonings the most successful movie of all time: from initial outlay of just $1.2 million, it has to date grossed $140 million in North America alone. It also holds the record for the longest-running continuous theatrical release ever, after the Waverly Theatre in New York ran it in 1976 as a weekly midnight movie in whose word-of-mouth popularity grew, then snowballed, then went national and international. It's the ultimate cult movie.

Rocky Horror fandom, centred in the United Kingdom around the excellent Time Warp website, works on two levels: part-timers who turn up once or twice a year to a Rocky Horror party, a screening or a performance, dress up for the occasion and know a few of the audience participation callbacks and throw the rice and the water, and people whose entire life is defined by their obsession and whose calendar is built around conventions and gatherings.

Those callbacks (one inventory of which can be found here) are a controversial issue, especially at the stage musical. Ade Edmondson, who served a stint as Brad, told Richard O'Brien “It's all very well them shouting out lines, but their timing isn't very good, is it?” O'Brien himself, interviewed by Paul O'Grady in 2009, admitted that “Sometimes it can overload the show... It's like going to a party you've not been invited to, if you're not careful.”

A more creative manifestation of fan-love, perhaps, are the Shadow Casts. These are not, as the name would suggest, a revival of Philidor's phantasmagorias of revolutionary Paris, but showings of the film at which amateur actors 'perform' every scene beneath, or in front of, the screen. Fandoms which foster unbreakable bonds and lifelong friendships between their followers are commonplace nowadays but the cult of Rocky Horror was one of the first. At its worst, it's every bit as annoying as Simon Pegg/Tim Bisley thinks. At its best, it's beautiful.

It's the fan culture surrounding the film, as much of the film itself, which appears to have presented an obstacle for critics over the years. Garry Mulholland, in Popcorn: Fifty Years Of Rock'N'Roll Movies, described Rocky Horror as “like an alternative stag or hen party”, and there's no denying that this criticism sticks, to some extent. Rocky Horror indubitably provides a 'safe space', an adult creche where transgressive behaviour and cross-dressing are accepted, nay, encouraged. Rocky Horror is a set of stabilisers on your sex bike, a pair of water wings for your first swim in the sea of depravity. But is that such a terrible thing?

A similarly negative view was expressed in Glam! by Barney Hoskyns, who saw Rocky Horror as a 'travesty' which “simply diluted the original outrage of the Ridiculous Theater companies, as well as the films of Warhol and John Waters”, going on to approvingly quote Phil Dellio and Scott Woods' I Wanna Be Sedated: Pop Music In The Seventies: “The Tubes and The Rocky Horror Show dealt the genre a serious blow by trying to satirize something that was partly conceived as satire from the outset”.

Other theorists, however, have taken a more favourable view. Alwyn W Turner, in Glam Rock: Dandies In The Underworld, posited Frank-N-Furter's character as a potent instance of camp as a weapon. “Bowie had worn a dress, but the sight of the pouting Curry in a corset, suspenders and stockings was even more transgressive: a male assault on Weimar, dressed by Frederick's of Hollywood, that somehow turned Curry into a sex symbol of the times.”

On the back of the film's popularity, the stage musical which gave birth to it has itself become an enduring favourite whenever it tours, with a casting policy invariably based on the gag of dressing up a well-known face (Antony Head, Jason Donovan, Craig McLachlan, Sebastian Bach) in stockings and suspenders. Other famous names who have served time on the show include Joan Jett, Penn & Teller, Jerry Springer, Tim McInerny, Robin Cousins, Craig Ferguson and Edward Tudor-Pole. There has even been talk of turning the musical into a film again, with Fox rumoured to be planning some sort of fortieth anniversary remake, but it's gone very quiet since the story first broke in the spring. Perhaps they've glanced at another doomed attempt to recapture some of that Rocky Horror magic, and sensibly taken heed.

Because, if The Rocky Horror Picture Show has its flaws, and it certainly does, then its sort-of-sequel, Shock Treatment (1981), was nothing BUT flaws, stitched together. The initial pitch was a straightforward sequel with Frank reanimated as a zombie, but the unavailability of key cast members Curry, Sarandon, Bostwick and Adams (either through choice or clashing commitments) forced O'Brien and Sharman to conceptualise an entirely different beast, as did a strike, which forced them to move production from the planned US locations to a UK studio. Set in a television station in Denton, its action takes place between a TV game show and a mental hospital, with a cast featuring several Rocky Horror survivors (O'Brien, Quinn, Campbell, Gray), the great Barry Humphries, and a pre-famous Rik Mayall and Ruby Wax. Mark Kermode, one of Shock Treatment's very few high-profile fans, has called it “a horribly prescient tale of the rise of reality TV” which, to be fair, it is. Unfortunately, it's also a bit rubbish. Or at least, it was: Shock Treatment has now made the reverse journey to Rocky Horror, turning from a film into a musical (which opened at the Kings Head in Islington earlier this year) with the blessing, and partial assistance, of O'Brien, and works far better in that medium.

It would be an overstatement to speak of a Curse Of Rocky Horror. After all, two members of the cast went on to enormous success. Meat Loaf released the record-breaking Bat Out Of Hell and became one of the best-selling rock stars in history. Susan Sarandon became one of the most respected actresses of her generation, and a five-time Oscar winner.

The film's lead, however, never entirely capitalised on his sudden stardom in Rocky Horror's aftermath. The young Tim Curry was intensely serious about his craft, and the former and future RSC actor (his next job was an RSC production of Tom Stoppard's Travesties) agonised over the likelihood that his breakthrough role would leave him typecast. As early as 1975, he told STOIC (Student Television Of Imperial College), “I was hesitant in that, if it worked, it might be a difficult image to shake off,” and that “It got a bit tiresome, playing such a strong character. It threatened to take over.” He was right.

Not that his immense talents haven't been in demand. He's excellent as the butler in Clue, the hapless suitor in Oscar, and the late night DJ in Times Square, to name but three. He also found success as Pennywise the clown in Stephen King adaptation It, and as King Arthur in Monty Python's stage show Spamalot. He even had a sideline as a recording artist, making three little-heard and faintly bizarre albums in the Seventies and Eighties. In 2012 Curry sadly suffered a major stroke, but has continued to do voice work while in recovery. He will, perhaps, go down in history as an actor who never quite found his place.

Patricia Quinn also views Rocky Horror as a partial albatross. “People don't take me very seriously because of it,” she accepted on the director's commentary, “but I would never not have done it”. She's worked steadily since, but hasn't left Rocky Horror behind, often attending fan conventions. Tellingly, she now has the red hair for real that was her character's trademark. Barry Bostwick has also never wanted for work, notably landing a major role in Spin City. Other cast members, however, abandoned acting completely. Little Nell, after a short-lived pop career, became a nightclub proprietor and restaurateur. Peter Hinwood had one further role in Sebastiane, then quit showbiz to become an antique dealer.

Richard O'Brien himself, now living once again in New Zealand, has rarely stopped working, notably presenting Channel 4's hugely popular The Crystal Maze and playing The Child Catcher in the West End production of Chitty Chitty Bang Bang. He keeps Rocky Horror on a long piece of elastic: he's not always closely involved, but never entirely lets go. (This September, he will be playing the narrator during the current production's run at London's Playhouse theatre.) In 2012, he told an interviewer that he considers himself transgender/third sex, that he had been using oestrogen for a decade, and that he was probably 70% male and 30% female. For all the cheap jokes Rocky Horror derives from sexual ambiguity and gender fluidity, O'Brien himself is no opportunistic outsider cashing in: he's the living embodiment of “Don't Dream It, Be It”.

Perhaps there is symbolism in Rocky Horror's chaotic ending. It is Frank – well, Frank and two unfortunate minions - who dies. Everyone else has been liberated: from servitude, and from repression. It's too much to expect one film, even one with the cultural clout of The Rocky Horror Picture Show, to liberate us in the same way. But for a couple of hours, once in a while, it can make you taste that unfettered freedom.

Sure, it all seems a little quaint now. We live in a time when another film dealing with unconventional sex, 50 Shades Of Grey, has been bumping up Ann Summers' profit margin in a similar manner to Rocky Horror, while leaving movie theatres in a far worse mess (with vomit and blood on the carpets instead of rice and water). But make no mistake: in its time, Rocky Horror was a transformative force which, O'Brien in the DVD commentary, “released people from their male-female parameters”.

On a similar theme, in the programme notes for the 1996 tour, the creator railed against “sexual ghetto building”, concluding that “it's time for us to tear down the walls that we build between ourselves, and allow individuality to flourish in the spirit of true libertarianism. It's time for humankind to become more gentle; the barbarians have had the planet for long enough. So, if you want to slip into a little black number with shoestring strap, feel free, for it is written (now, anyway) that no army ever marched in anger wearing fishnet stockings and six-inch high heels.”

Put that in your bag, Simon Pegg, and boil it.