I don't know what the Prime Minister's plans are this weekend but should he find himself in receipt of a few idle hours I would urge him to hotfoot it over to a branch of the excellent Picturehouse cinema chain in either Clapham or Greenwich. There he can see the superb new film Treacle Jr, which explores the friendship between an incorrigible (and often comically unintelligible) Irish goofball (Aiden Gillen) and a lanky out-of-towner (Tom Fisher) who is sleeping rough after deserting his wife and child.

I know Mr Cameron takes a keen interest in new British films -- he's quite the cineaste, having expressed enthusiasm recently for The King's Speech. (Never let it be said he doesn't go out on a limb in his tastes.) Oh, the delicious and unselfconscious irony in celebrating a success that would not have happened as it did without the UK Film Council, which Cameron's government then killed off in an act of staggering short-sightedness and philistinism.

That said, what looked like a clueless bit of axe-swinging did begin to assume a certain obscure logic once I listened to a news item this week about St Basil's Cathedral and heard for the first time the story of how Ivan the Terrible was rumoured to have gouged out the eyes of the architects after the cathedral was completed, so that they might never again create something of comparable splendour. Could The King's Speech be to St Basil's Cathedral as David Cameron is to Ivan the Terrible?

But back to Treacle Jr. The Prime Minister will doubtless be aware that Jamie Thraves, the film's writer-director, found acclaim eleven years ago with his debut feature, The Low Down. That picture was an atmospheric tale of aimless twentysomethings haunting the streets, pubs and walk-ups of Dalston, east London. Treacle Jr is shot through with some of the same amorphousness and melancholia, as well as the earlier film's attentive use of locations (south London this time) to nourish characterisation. In Gillen's eye-catching, lapel-grabbing, jaw-jabbering performance, Treacle Jr also features the sort of scene-stealing work on which voters can seize helpfully come awards time. Fisher is also excellent in the much quieter part, effectively the straight man to Gillen's tomfoolery.

I only bring the Prime Minister into all this because it just so happens that Treacle Jr is being released on the same day as Harry Potter and the Deathly Hallows Part 2 (which I reviewed last week). That's two British films, both admirable pieces of work in their own ways, situated at opposite ends of the budgetary spectrum. One will have a release supported by limitless publicity and advertising before opening with a screen count well into triple figures, as one would expect from a major studio's blockbuster-to-end-them-all. The other is arriving on two screens, with more to come if it proves a success -- which is why, if you are intending to see the movie (and you should), then it's imperative you go this weekend to guarantee it doesn't drop off the circuit.

Cameron could really do his bit for the UK film industry here. It's all very well championing the Harry Potter films, as he did late last year. That's the easy bit. The franchise is already popular and cherished, and it has provided extended employment for hundreds, if not thousands, of people. Cameron's support of it brought to mind Giles Smith's analysis (in his book Lost in Music) of a pre-1997 Tony Blair's admission of musical preference:

[A]sked in an interview what kind of pop music he liked . . . Mr Blair came up with REM, Seal and Annie Lennox . . . If the party had commissioned an expensive advertising agency to spend seven months in collaboration with a public relations firm researching this declaration, it's hard to believe they would have come up with anything so beautifully poised. REM, Seal and Annie Lennox: an American rock group and two British singers, one black male, one white female, with fingers in pop, soul and dance, an ample musical spread, economically achieved . . . Note how the balance tips in favour of the British artists, to avoid the suggestion that Mr Blair might be somehow in thrall to American culture.

Smith goes on to identify the tinge of the mainstream and the modern in Blair's choices (which went on the record pre-Britpop); these suggest implicitly that the future PM was no dinosaur, and no elitist either. Would that Cameron were so sophisticated. All he does is plump for the blindingly obvious, the populist choice that not only needs no leg-up from him but which no potential voter could respond to with belligerence or bewilderment: no Middle Englander, if such a creature still exists beyond the grounds of Hogwarts, would be heard exclaiming "Harry who?" or "Why on earth didn't he promise a generous stipend to Terence Davies?"

Cameron could rehabilitate himself now by coming out in support of Treacle Jr, which would show not only an enthusiasm for vitality in British cinema, but an ideological consistency on his part. After all, what could be more resourceful, go-getting and Big Society-esque than re-mortgaging your own house to make a film? That's exactly what Thraves did to raise the majority of Treacle Jr's £30,000 budget (as he tells Time Out here).

The one very real danger in soliciting Cameron's endorsement is that it could deter audiences from seeing a film they would otherwise have greatly enjoyed and admired. Anyone who was young in the 1980s will remember Margaret Thatcher praising the band Thrashing Doves on Saturday morning television. Chris Briggs, head of A&R at the group's record label, put it best: "What worse thing could happen to a young band than having Thatcher tell the nation's youngsters they were jolly good?"

"Treacle Jr" is released on Friday. To find one-off screenings of Treacle Jr accompanied by Q&A sessions, go to www.nbcq.co.uk