Fortunately, there are enough far-sighted producers around to know that with his track record (Bliss, News Hounds, Bad Behaviour, Jump the Gun) Blair doesn't need a script, just time to work up a story with a hand- picked cast.
This technique has inevitably led to comparisons with another Salford- bred film-maker, Mike Leigh. Indeed, Blair produced Leigh's first film, Bleak Moments. But Blair does not especially welcome the link. "I don't think Mike Leigh and I have a lot in common. There's obviously a certain kind of neo-realistic or naturalistic relationship to real life, but our films are different things."
The fruit of Blair's latest improvisation is an intriguing meditation on what motivates stand-up comedians. Phil Daniels (right) a long-time Blair collaborator, plays Alun, a cocky Cockney comic with a serious addiction to gambling and danger. Having breezed through one gig in Glasgow, he decides to spice up his second by abusing his audience. "We get a lot of Scottish comedians coming down to London," Alun sneers. "We usually recognise them by their catchphrase - `can you spare any change?' `Yeah yeah, just don't breathe on me'."
"Statistically, you're less likely to die in a car crash than you are from buying your dinner at a Scottish cooked-meats counter. What a horrible way to die." Talk about a fast track to suicide. Blair explains the thinking behind this self-destructive tirade. "They say that with gambling, winning is the wrong answer. If you win, that's the end of the story, and you don't want that. The right answer is to be punished by losing. There seemed to be a nice little link to stand-up there. If you go on stage and successfully make an audience laugh, what do you do next? Maybe you make them hate you."
Daniels and Blair worked up the character over a three-month rehearsal period. "Phil was nervous at the beginning because he knew I'd ask him to do gigs to get experience," Blair chuckles. "Stand-up is so different from acting because there's no character to hide behind. Phil did a couple of gigs in London alongside Harry Hill, Jo Brand and Mark Lamarr, which he found very brown-underpanty. But then he got a few laughs and started to enjoy himself.
"At the beginning, working on my films, all the actors can see is this expanse of nothing. But once they get over that initial yawning chasm and know who the characters are, the actors always start to enjoy it. They like showing off."
A genial, greying man, the director rejects the charge that building up a character through improvisation is self-indulgent. "It's actually very efficient in terms of short shoots because the actors end up knowing as much about the characters as I do. We spend less time talking about motivation. I can leave that to the actors and concentrate on the technology."
Next up, Blair is contemplating making another film by the same means, this time set in Armagh. However it turns out, one thing it won't be is mainstream. "I do feel an outsider in the sense that I plough my own furrow and try not to compromise," says Blair.
But wouldn't he ever fancy a crack at Hollywood? "I'd do a big-budget film there if they'd let me improvise. But I suspect they wouldn't. It would end up being about a bunch of New Yorkers rather than people surfing and sunning themselves on the West Coast. I'm much happier working on smaller-budget films. I want to make films on a human scale. I'm interested in people, not pyrotechnics."
`Stand and Deliver' is at 9.55pm tomorrow on BBC2