Full scale psy trance rave near The Den; reggae soundsystem strung up down an alley in Deptford; A midsummer night spent in the yard of Sanford Housing Co-op – There's something about the less-frequented streets of south east London that encourages these happenings, a sense of potential. Maybe it's because the roads that move between the industrial units and suburban estates feel unwatched, or less watched, leaving opportunity for a little subversion. Tonight there's a party in an office complex off the Old Kent Road, where a group of DJs and their crowd can play music and move freely, out of sight and undisturbed (for now).

2.30am: 'Givenchy', the opening track of Rich Gang's 'Tha Tour' mixtape plays out, all soft bass bumps 'n blue sky brags. Then there's a U-turn into splintered, breakneck tekno that convulses wildly, pushing the soundsystem into the red and filling the room with pressure. Shanti's playing and the sudden switch in atmosphere he creates feels exhilarating. It's unpredictable, brave, aggressive and fun as fuck. Something you should hear more of from DJs playing in London but don't. Not at the city's 'experimental' club nights let alone its regular clubs.

But then this party – Endless – and the venue it's held in tonight are neither of those things. Triumphant rap plummets into nails rave because why not? The approach of the DJs who play here is non-linear and non-ironic, with things like dancehall, reggaeton, rap, black metal, noise and plenty home-brewed productions all moving across one another constantly. As a dancer you're exposed to sound that's hyper sexual, hyper aggressive but also super sensual, as likely to be treated to a Chicago bop banger as you are wrapped in a drone that's lined with slivers of melody. It's an underworld away from the Resident Advisor listings section and there's a sense of freedom that extends beyond the intersection of seemingly disparate genres: no bouncers (no surveillance), BYOB, everyone dancing from the front of the room to the back, near darkness inside.

Lexxi's been running it out of venues and spaces in the south of the city (and sometimes north) for the last two years. His chosen spots are mostly hidden away or overlooked, though he says that's not intentional – he just throws parties wherever he can. "The club should be an escape," he says. "A lot of the time in London it's more about networking and your look, which is cool, but Endless is more about just doing you." So tonight people arrive in anything from Cottweiler to sportswear to big black overcoats because it's still cold outside and the windows that run the length of one wall quickly steam up as the dancefloor moves in time to every ebb and flow. Music comes from laptops placed on a small table in between two speaker stacks and everyone who plays does so with their back to the audience. It's like a house party. You can see audio files being selected, loaded, blended into one another with the sweep of a cursor. The system peaks constantly, coating digital files in anarchic fuzz.

3.15am: The relentless mechanical stabs 'n pounding bass bumps of 'Paleta' are launched from the speakers by Kamixlo. Though still only a SoundCloud upload, it's one of the fiercest club tracks of the year and a devastatingly good example of what the artists who assemble at Endless are capable of. "I usually book the club, then friends DJ and perform," Lexxi says. "Anyone who's about really, anyone who's into the same thing." As well as he and Kamixlo, Nkisi, Blaze Kidd and Uli-K are all regulars, with guest bookings that include fellow Londoners Endgame and Larry B, as well as overseas heads WhyBe, E+E, Total Freedom and Mykki Blanco (who turns out a red-hot freestyle at some blurred point during this evening's proceedings.) Hit SoundCloud and you'll find a wealth of productions and mixes, along with further affiliates such as Palmistry and Chino Amobi. Everyone's bending things in a different direction. Endless wormhole.

A great entry point to this squad is Blaze Kidd's 'Exclusivo' mixtape, which was uploaded to SoundCloud and Mediafire in November of last year. The South London vocalist raps in Spanish and likes to ride the downtempo, waist-winding rhythm of reggaeton. Uli-K, Palmistry, Kamixlo, Endgame, Shanti and Lexxi all contribute productions to the tape, each giving their own take on the music that's synonymous with Blaze's Ecuadorian background. "Reggaeton is a massive scene in Latin America," he says. "We love how it sounds, so we make our own stuff out of it." 'Angel' with Uli-K (and Sirpixalot) is so sensitive but so hard, a love song bottled during an electrical storm; 'Lento' with Lexxi is exactly what you want to hear at the end of a long night spent dancing with a lover, the perfect excuse to get close and make libidinal movements in the dark; 'Calidad' with Shanti is unapologetically cathartic, Blaze's lyrics moving nimbly over thundering boom 'n klang; 'Me Acuerdo' with Endgame is a triumphant party jam. The tracklist goes on. It's all excellent, forged by sheer creativity. And it all clicks together, even though over 10 people worked on it. "Everyone's production on it is some of their best," says Kamixlo. "It's funny because nothing was ever said. It wasn't like, 'make this type of thing.' Everyone made what they thought was going to fit."

3am: Blaze Kidd runs through a medley of his own tracks and they sound raw in this context, far removed from the safe space of a SoundCloud playlist: one microphone, no monitors, a volley of lyrics launched into the black air above our heads. Dressed in a princely black designer tracksuit and flanked by close friend and collaborator Uli-K, he looks very much the rapper with a cause.

Music that can be filed next to 'Exclusivo' is appearing at a rapid rate. Endgame's debut 12" just dropped via Lisbon's Golden Mist and it contains an ice cold and utterly enticing collection of instrumentals (plus one vocal track by Blaze) that are all set around the 100bpm mark. Lexxi self-releases .wav files via his Sellfy profile, where you can download searing club cuts like '5 X' and 'Scrape' for 90p, and will put out his first EP soon. Nkisi has linked up with Chino Amobi and Angel-Ho for a project called Non, which will act as a platform for the trio and has just unveiled its first set of free downloads. After an excellent run of singles, EPs and mixtapes, Palmistry is working on a debut album. Shanti released a powerful, psychedelic mixtape as Bekelé Berhanu on Janus earlier this year. And then there's Lexxi and Endgame's NTS radio shows (called Endless and Precious Metals respectively) which are used to air unheard material and guest mixes from artists operating within their networks and beyond.

1.15am: Lexxi's kneeling in front of his laptop, picking out a stream of tracks that dip and dive unpredictably. One moment he's sending a hot dancehall beat into a cloud of static, allowing percussion to be enveloped by noise, the next he's summoning monster guitars riffs out of nowhere. Playing to extremes.

It doesn't feel like there are any boundaries, but he disagrees: "It's just to do with our taste. Generally the music is a bit harder and more raw than most other nights." Maybe that's why Endless feels so refreshing: it doesn't follow the same aural narrative as any other London party at all. "When Uli-K's playing tunes off his laptop, it's like my perfect club set every time," says Endgame. "It goes from black metal to K-pop without worrying. It's not rebelling, it's just what we're into on a very honest level." And perhaps Kamixlo puts it best when he says that he finds it "so dusty when a party is set to a particular type of music – it's so boring."

This edition of Endless is a DIY effort. Empty space. Someone's soundsystem. Illuminated by a single green lazer that traces along the ceiling and the intermittent flashes of a strobe light that's been left on the floor. Laptops and a line in. Turn up. Endless is where you'll find crucial music. And it's evolving: a label will soon start, kicked off by releases from Lexxi and Kamixlo. The radio show lands monthly on NTS. New venues for the party continue to be scoped out. Watch Facebook or SoundCloud bios for information, as and when it appears.

3.55am: Blue light flashes in through the venue. A police van has parked outside and its presence is enough to put out the party. But no one seems that bothered: the night's been lively and the officers haven't come into the space, as has happened before. Plus it won't be long until the next function, a few weeks at most. "I guess we always break the rules," says Blaze Kidd afterward, while chatting about everyone who plays at Endless. "Nothing can stop us."

Find out when the next Endless is by checking the Facebook page