Lindsay Anderson's bleakly subversive classic If… has frequently been cited as an influence since its release in 1968, but surely none ever sounded quite as incongruous as when David Cameron professed his admiration for the film on the Today programme last week. Granted, it's set in an exclusive public school similar to his alma mater, and the sudden lashings of ultraviolence might have brought back fond memories of Bullingdon Club exploits, but the film's incendiary spirit and withering critique of the class system are hard to square with someone who once proudly admitted to sleeping out on The Mall so as to ensure a prime spot at Charles and Di's wedding. Still, it seemed for once like an honestly held opinion, devoid of apparent spin or political calculation, and for a while there I almost felt my deeply entrenched antipathy towards the man begin to thaw. Almost.

Thankfully, normal order was swiftly restored, and with his latest trite and patronising advice to British film-makers to make “more mainstream" movies in a speech at Pinewood Studios this week, Dave has once again incited normally calm and rational people into a pique of blood-boiling rage. On Twitter, the public backlash is already in full flow, while veteran director Ken Loach has led the early voices of dissent among film industry insiders. Hidden behind the lofty rhetoric about making the sector “more dynamic and entrepreneurial", the real agenda quickly surfaces – to divert funding away from independent cinema, with its potentially niche and challenging releases, towards more commercially viable propositions.

It's difficult to avoid the suspicion that Cameron's sentiments are rooted in ideology: state subsidies to fund the arts are anathema to the Thatcherite creed, particularly when lottery money is being used to bankroll the sort of social realist movies beloved of the arthouse-frequenting Guardianistas who are the natural enemy of any True Blue Tory. Demonstrating his usual unwavering faith in the economics of supply-and-demand, he went so far as to suggest that funding should be apportioned according to box office potential, a notoriously nebulous concept. He's backed in this by Downton Abbey creator and Conservative peer Julian Fellowes, a member of Lord Smith's review panel due to publish their report into government policy on film funding on Monday. "There has been the thinking in the past that public money should only go into films that can't get any investment anywhere else," Fellowes told Sky News. "When you actually analyse that it means it should only go into films that nobody could conceivably want to see and there's no logic in that - you want to make a film-friendly, audience-friendly industry."

There's plenty to take issue with there: the suggestion that films which struggle to find investment are de facto  films which no-one wants to see, for starters. Slumdog Millionaire, the sort of unqualified British success story which Cameron was presumably referring to, endured a difficult gestation period  and seemed destined to go straight to video after Warner Bros. closed its independent film division in 2008. A last minute joint bail-out deal between Fox Searchlight and Warners secured a theatrical release, and the rest is history.  The King's Speech, the UK's second-highest grossing movie of 2011 (behind the Harry Potter finale) is another case in point: a film which in retrospect looks like a sure-footed triumph with impeccable box office pedigree, but in reality was a difficult sell (speech impediments? Not very Hollywood), and owed its very existence to funding from the now defunct UK Film Council.

Do Cameron and Fellowes truly believe that the box office potential of a movie can simply be gauged by a series of crude calculations? Any casual observer of the UK box office will recognise this as palpable nonsense. As Ken Loach pointed out to the BBC: "If you knew what was going to be successful before you made it, we'd all be millionaires. It doesn't work like that."

The worrying implication of all this is that, with a government policy which incentivises profit, aspiring British filmmakers will be forced into a creative straitjacket, reduced to knocking off feeble period dramas and derivative gangster flicks which already have a core and readily identifiable audience. The risk-averse strategy which has already ensured our multiplexes are cluttered up with prequels, sequels and reboots will be perpetuated. A creative environment where filmmakers are hamstrung by the risk of commercial failure will make it increasingly unlikely that the next Shane Meadows or Andrea Arnold will be unearthed.

UK filmmakers have long pined for a state funding model for indigenous cinema similar to that of France, where taxes are levied for specific use as subsidies for movie production. But with the coalition's relentless austerity drive and last year's controversial abolition of the UK Film Council, that dream seems further off than ever. And yet, despite everything, 2011 represented something of an annus mirabilis for homegrown cinema, with The King's Speech and The Inbetweeners movie conquering all-comers at the box office, and critically acclaimed low-budget releases such as Submarine and Weekend proving solid word-of-mouth hits. But, with TV and DVD revenues falling, and potential financial backers now in short supply, the long-term omens aren't good. The lottery funding model wasn't perfect – with right-wing tabloids eager to reel off a list of box office flops at any given opportunity as an example of profligate state excess – but it presented a real opportunity to develop new talent, insulated to an extent by commercial imperatives.

And what if Cameron's beloved If… were released today? Well, it's difficult to conceive of a film less likely to meet his stringent criteria for mainstream appeal. With its problematic subject matter, penchant for extreme violence and frequent segues into surrealist sequences, it most likely wouldn't even get past the pitching stage. A shame.

Still: there's always that Harry Potter reboot in the pipeline, right?