Jasper Rees meets a lawyer who swapped silk for paper
Peter Moffat is a barrister turned playwright. Natural affinities between the professions abound - there are laws in the theatre just as there is theatre in the law.

The Radio Four comedy Chambers, the second series of which started on Monday, is written by barrister Clive Coleman. Clive Anderson has taken a parallel route into gag-writing. Moffat is the only one not mining his experiences of one profession simply to create light entertainment in another.

Nabokov's Gloves, which previews at Hampstead Theatre this week, is a jolting saga of conscienceless barristers who will sell themselves to the devil to secure a not-guilty verdict. Take Nick, who in his summing- up will borrow the death of someone else's father and pretend it's his own story to create the illusion of caring. His colleague Joe neglects his own scruples to trade on the jury's homophobia. Darling - so called because that's what she calls everyone else - will throw on a Wonderbra if she thinks that it might swing the male members of the jury.

"I'm stunned in retrospect at how well I used to sleep," says Moffat. "A good 80 per cent of the people I represented were, in my opinion, guilty, but it's utterly understood what you're at. The probably experienced criminal knows not to say the wrong thing. You know not to ask the wrong thing, and the fact that he's almost certainly guilty never gets touched."

We meet in the dressing room at Hampstead Theatre, a factory of disguise. The law is every bit as concerned with the dramatic role of costumery. Moffat says that "the glamour factor" - the gowns and wigs - "really really works, because people go quiet", just as when the house lights go down. But in Nabokov's Gloves Moffat has eschewed the chance to re-enact the lulling rhythms of the courtroom in favour of a kind of Noises Off with wigs on. From the opening scene, in which Nick, summing up, is shown to be addressing his reflection in the mirror, the play digs beneath the performance - the scriptedness - of cross-examination.

Although the law firm is a slick staple of American film and television, it is rarely visited in British drama. "It is much more interesting than we have seen hitherto," says Moffat. "In a barristers' chambers there are 35 people, most of whom have got enormous egos, dealing with people in crisis. This Life sort of wasn't about lawyers; it was about people in their twenties being on telly and swearing. But I think you could do that with some bloody exciting stuff about the law as well. Somebody could really do it on telly."

That somebody could be Moffat himself, who has a treatment on someone's table at the BBC about a radical stable of Edinburgh advocates. In the mean time, his X-ray of barristers backstage finds clever minds content to trade in intellectual trivia. The play's title refers to the fact that Nick knows that Nabokov was a goalkeeper. He and Joe are contributors to a music encyclopaedia. In other words, in front of a jury they get drug-pushers off the hook, then it's back to football and pop.

Whenever he wasn't in court, Moffat was writing. One vocation had to give. The switch was "financially disastrous" - having left the bar two years ago, he now works in cafes. But he seems to have made the switch at least partly as a means to moral replenishment. He did his pupillage at John Mortimer's chambers and moved to left-wing chambers "for good political purposes. You want to cross-examine police officers. But seven years in you're representing Mr So and So who beats his wife. Michael Mansfield and Geoffrey Robertson can choose cases, mark out a political career. Underneath that, you get what you get."

If there is a character Moffat identifies with in Nabokov's Gloves, it is Joe, who has a conscience which he airs at dinner parties but disregards in court. "I understand Joe professionally - the struggle he has with the morality of what he does. But as Nick says to him: `There's only one question. Does the system work? If the system works, shut up and get on with it.' " Joe is upbraided for making a spectacle of his misgivings. "People do get misty-eyed when you tell that sort of story, and you should ask why you are telling it. Because the next day you are going to do it again. You're telling it as a way of making yourself more interesting, which is a bit shameful."

`Nabokov's Gloves' previews at Hampstead Theatre, London, from tomorrow, 14 May.