I enjoyed Billy Elliot. It was lovely and humane, and a lot like many other films I've seen

Once a new art form is invented and established, an infrastructure develops to maintain it: a college to train people to do it, buildings dedicated to it, professional guilds, awards, grants. But, like anything else, art forms can become defunct. This is especially true of forms that depend on performance: masques, mystery plays. W H Auden's first published work, Paid on Both Sides, is a "charade", written to be performed in a country house. "The country house charade is among the most living drama of today," he wrote, ludicrously.

Sometimes a form can be dead, but won't lie down, remaining propped up by its infrastructure. Even while working as the jazz critic for the Daily Telegraph, Philip Larkin believed that jazz was dead, "dead as the Gregorian chant". He believed that it had moved so far away from anything that could be described as jazz that it had become something entirely different (and he hated it). He may have been right, or maybe he was just growing old. And there can be another problem with experience, or growing old, or however you describe it. When Clive James gave up his TV column in the Observer, it was, he wrote, partly because he was tired of old ideas coming round again and being greeted as new ideas.

I went to see Billy Elliot this week at my local multiplex. Stephen Daldry's debut film has been acclaimed by some people as the greatest British film ever made. It has been a huge financial success, and looks as if it will win a sackful of Oscars. I choose this example because it is a film I liked. It is beautifully made, superbly acted, cleverly written and I sobbed throughout. But the truth is that this film is entirely constructed out of other films. Now, I know all the arguments about how Shakespeare borrowed virtually all his plots from other people, about homages, or rather hommages (it sounds so much more acceptable in French), but still . . .

Let me give some examples. I assume that everybody knows the very simple plot: a boy in a mining community during the 1984 miners' strike develops a passion for ballet. Will he win over his father and brother? Will he get into the Royal Ballet School? The story is Kes remade in the affirmative style of The Full Monty (the borrowing of the boy's older brother from Kes is breathtaking, as is the imitation of the final freeze-frame from The Full Monty). The Full Monty - ex-miners redeemed by stripping - was itself almost identical to the slightly tougher Brassed Off - ex-miners redeemed by brass band. I would love to have been at the pitching sessions in which somebody told the story to a movie executive and the executive said: "Oh, that's a good idea."

Then there is the genre of the middle-aged teacher running a class in some dusty hall or schoolroom, clinging on to lost ideals, possibly redeemed by the student or students. Julie Walters, who plays Billy's ballet teacher, has been in a couple of such films: Educating Rita (English literature) and Stepping Out (ballroom dancing). Through his theatrical career, Daldry must be most acquainted with the tough political version of the story in Trevor Griffiths's Comedians.

Then there is the sub-genre of the audition scene, in which the stuffy professors are startled by the unconventional performance of the young genius. Obvious examples are the opening sequence of Fame and the closing sequence of Flashdance (also about a working-class young person with dreams of becoming a dancer). In the case of Billy Elliot, more subtly, the professors are impressed not so much by Billy's dancing as by his touching description of why he dances (which struck me as reminiscent of Eric Liddell's lines in Chariots of Fire about why he runs). And I could go on and on.

I am torn by my reactions to this film. In many ways, I thought it was lovely and humane. If it is sentimental and soft-edged, then it's in a good cause. I can imagine it educating a generation of boys out of their attitudes of conformity, philistinism, homophobia - or at least it might if they weren't banned from seeing it by its ludicrous 15 certificate. Thank God for videos.

But isn't there a problem here? What happened to real life? It reminds me of the introduction given to Dennis Wheatley, the author of books about the occult such as The Devil Rides Out, when he once came to give a speech at the Oxford Union. The chairman declared himself a great fan: "Not only have I read all Mr Wheatley's books; I have also seen the films on which they're based."