The relationship between cinema and television was changed 15 years ago with the launch of `Film on Four'. Not just because television ceased to be merely a consumer of films but, as Sarah Gristwood argues, because it created some of the finest of our contemporary movies.

The list goes on almost indefinitely: Trainspotting, Four Weddings and a Funeral, The Madness of King George, Secrets and Lies, Mona Lisa, The Crying Game, My Beautiful Laundrette, Wish You Were Here. The credits belonging to Film on Four, the feature film arm of Channel 4, includes many of the pictures that have helped to make the current renaissance in British cinema a reality.

Like the channel itself, Film on Four is currently celebrating its 15th birthday. It's marking the occasion with A Splice of Life - a documentary (well, more a compilation of clips and quotes) to be shown on Christmas Day.

Hanif Kureishi (who wrote My Beautiful Laundrette) looks back to the beginning, in 1982.

"There were a lot of talented people around. The one thing that wasn't around for British films was money."

"When Channel 4 came in, it gave an enormous push to the film-makers," says Ismail Merchant, of Merchant Ivory. Needless to say Channel 4 had money in some of their productions (Howards End, A Room With a View).

Of course, besides the famous success stories, their list includes an awful lot of lesser movies, the names of which have passed from memory. And Channel Four Films (as they are now known) have even been increasing their output recently. Some 20 films a year should share a proposed pounds 28m in 1998, and pounds 32m in 1999. That's never going to mean 20 hits on the scale of Trainspotting, but it's still a huge gift to the film industry.

Perhaps, too, one should point out that many of the films credited to C4 were only partly financed by them. While Trainspotting was all theirs, they paid only about a third of the budget for The Crying Game, a quarter of Howards End, a quarter of Four Weddings and a Funeral. But they rewrote the relationship between film and television, commercially - in the sense that television ceased to operate only as a consumer of cinema product - and perhaps artistically. Danny Boyle, the director of Trainspotting, says that watching Neil Jordan's 1982 Angel in the Film on Four slot was "very inspirational. Here was a subject that was absolutely the province of television" - the Troubles of Northern Ireland - "made cinematic".

"It wasn't just that they came in, it was the way they came in," says Nick Powell, whose Palace Pictures had an extraordinarily fruitful (albeit sometimes edgy ) relationship with Channel 4. "They were not business led - they were led by screenplays, stories, film-makers."

Don't pursue money, and with luck it will pursue you. Four Weddings took some $250m dollars around the world. Not bad when you consider even what the channel's cut of that must be.

Film on Four had been in the cinemas for several years before they were joined perforce by the BBC. Score yet another one for C4, really ... And the BBC did not, until recently, commit to cinema so seriously. Their preferred path was to send a film into the cinemas only after it had proved itself on TV. Though that, witness the American success of Cold Comfort Farm - can work successfully.

As to what it is that Film on Four do so right, their very eclecticism seems to be the key. That's why no one could ever reasonably cast the bad films up against them.

"It's only because of our failures that we also have our successes," says David Aukin, who took over from David Rose in 1990. He talks of "critical mass" - a bulk of films solid enough for a few, at least, to be pretty well sure to be successful commercially as well as artistically. The alternative idea - to make fewer, more expensive pictures, putting all your eggs into just a few baskets - is something he has always regarded warily.

What scares him now, he says, is that people will use the recent success of comparatively low-budget British films to try to launch a wave of bigger British movies. "And that will spell disaster." Just as it did back in the mid-Eighties. Remember Chariots of Fire, and Colin Welland's Oscar- night cry of "The British are coming"? And what did come next? Big, bad, beached whales, such as Revolution and Absolute Beginners, that not only sank Goldcrest (remember Goldcrest?) but also put the fear of cinema-goers into the potential investors of the City.

Trainspotting was named by Variety as the most profitable film of 1996, in terms of its investment. Not that it took such a huge sum at the box office, but that it took 20 times its little budget. Aukin, last year, put the magic figure of pounds 5m as the viable budget for a British movie. Now Aukin is himself about to move on - to Miramax. His successor has not yet been decided. And the game may be changing again, with new sources of money opening up for film-makers - notably, of course, from the lottery.

There are probably questions to be asked about the decision by Channel Four Films to distribute their films themselves. And about forlorn directors who say that, yes, C4 put money into their picture and they are very grateful, but the company doesn't seem to have any plans for showing the finished product properly. And while Channel 4, over the years, has given invaluable support to many world-class directors such as Wenders and Tarkovsky, they are no longer prepared to buy in subtitled films in any quantity. Still, that's another arm of the organisation - and another story.

Wherever there is debate about the direction in which British film should be heading - more commercial? more adventurous? - Film on Four are, inevitably, caught in the crossfire. But look back over the last year or so and surely, overall, they have done outstandingly. Mike Leigh's Secrets and Lies with its cinema queues, its Golden Globe and Oscar attention; the box office success of Brassed Off, and The Pillow Book of Peter Greenaway; Fever Pitch, Alive and Kicking, Trojan Eddie.

On the subject of A Splice of Life, Mike Leigh voices one of the complaints you do tend to hear from - Danny Boyle's term - "the old guard". "There were, in my own opinion, some good aspects about the coming of Channel Four and some not so good ones," says Leigh. "The main thing that was a problem was that some of these film-makers, because of this pressure to make film that would be saleable in the States, and because of co-production and American money starting to creep in ... started to bend over backwards to make what I regard as quasi-Hollywood films."

Boyle is happy to put the other side of that story.

Change - "a constant revolution" - is a good thing, he claims. In this case, especially. "People now don't approach the idea of a British film with horror. They think there may be a genuine night out here." Channel Four films have done a lot to bring that about. Not bad, for a 15th birthday.