THEATRE / More, much more than this . . .: To put on a West End musical, Humphrey Carpenter had to write it, direct it and pay for it. That's fine by him.

Humphrey Carpenter has written, scored and co-directed two musicals; both his daughters are among the cast; it's costing him a neat pounds 16,000, all out of his own pocket. You could call his scheme to bring Babes and Mr Majeika to London for a four-day showcase a straight case of vanity staging. Or you could call it mad. With his through-a- hedge-forwards hair-arrangement, the hyperactive chatter of a runaway train and the effect of a mild hurricane, Humphrey Carpenter is every inch the mad professor.

Mad, but there's plenty of method in his madness. And mission too. Babes is a serious story of the exploitation of Judy Garland and fellow Hollywood child-stars; Mr Majeika is a pantomimic piece of wacky wizardry glancing at different attitudes to education. Both shows are performed by 60 amateur actors aged between five and 18, the Mushy Pea Theatre Company, and have been put together by a production team of volunteers, though the 20-piece orchestra is professional. Carpenter is happy to be footing the bill.

Like any sensible person looking for fame, fortune and a West End transfer, Carpenter invited Cameron Mackintosh to the opening. 'His mother's cleaning lady is also employed by my mother-in-law. But he rang up to say he wouldn't come because he hadn't been involved with the creation of the show. He wished us luck.' Happily, even without Mackintosh's patronage, Carpenter can afford to indulge in a spot of financial ruin. It's to fund such projects that he has written biographies of W H Auden, Benjamin Britten ( pounds 70,000 advance, banked), Tolkien and, currently (for a pounds 20,000 advance), Lord Runcie, the former archbishop of Canterbury. His enormously successful Mr Majeika books for children earn pounds 16,000 annually (and it takes him three days to write a new one). He may have an A-reg car, but, more importantly, he has paid off his mortgage and his two daughters are at state school. More amazing, the box office has taken pounds 5,000 in advance bookings. But the point of it all is that Carpenter has complete control - no patrons, no sponsors, no interference. 'I like making my own decisions. I'm selfish.'

Carpenter frequently refers to the selfishness of his vocation. This awareness of sin and candid confession of it are perhaps the legacies of being a clergyman's son, a matter he has been unable to forget this week. His father, former bishop of Oxford, died, aged 91, last Monday. 'Thank God for cold storage,' says Carpenter. 'I've been signing production cheques with one hand and death certificates with the other.' The show must go on; his father's final curtain will wait until the West End is won.

In the Mushy Peas (rhyming with slushy not pushy), which he set up nearly 10 years ago, Carpenter is (rather unselfishly) recreating the kind of fun that he, as a lonely, only child, found as a member of the Children's Pantomime Society run by a Dean's daughter in Oxford. Anyone can be a Mushy Pea. 'If they aren't much good, they drop out because they don't enjoy it,' says Carpenter. Mike Leigh-style improvisation was in the air and taking his cue from that and Monty Python re-runs that were required viewing at the time, Carpenter's improvised The Wizard of Oz featured the wizard as a Thatcherite housing-agent. His Peter Pan had bigger ideas ('No scripts, but a few fixed points') and was performed at the Cheltenham Literary Festival. After Alice in the Channel Tunnel, a pantomime frolic came Mr Majeika: The Musical with a script, a score (by Antony Royse) and a run in Chipping Norton. That did it. Carpenter wanted brighter lights, bigger cities.

'The obvious place is the Edinburgh Fringe, but you can have five people in the audience and you won't get a review. Then the Shaw fell into our lap. It isn't completely mad in that we're going to have decent houses. And frankly I think more people should do it: I don't see this enormous barrier between professional and amateur theatre. I think theatre is in the doldrums at the moment - all these glitzy musicals in the West End, all these worthy little touring companies doing terribly heavy stuff which makes me squirm in my seat.'

But why children? Quite simply, it's where Carpenter has found a niche. He tried writing novels and film scripts without success, but Mr Majeika was an instant hit, and was made into a television series with Stanley Baxter and Mirian Margolyes and screened worldwide. 'If you take it seriously,' says Carpenter, 'it's about a character who feels more sympathy with the child world than the adult world. I didn't intend to write that, I just wanted to write something commercial. On the whole, I find children more interesting than adults - I'm prepared to go that far. I don't think about it too much because it makes you terribly self-conscious. As for working with children, it's the adults I find harder to work with because they are powerful individuals who want to do their own thing.'

And why amateurs? Carpenter has worked with professionals in radio. 'They are very professional, very bored, poor things. I don't feel any need to use them. If we had Judy Garland as an adult played by an adult, something has gone immediately.'

But then Carpenter has always chosen the eccentric route. Having completed the BBC's general trainee course, he astounded everyone by choosing to present the Radio Oxford breakfast show for five years until he left to write biographies and devote more time to music - keyboard, double-bass, tuba and bass saxophone. He founded the band Vile Bodies, which recreates the dance music of the Twenties and Thirties, and is resident at the Ritz. He would fall into bed at 3.30am on Fridays, and be up at 9.00am to rehearse the Mushy Peas.

When pushed, Carpenter pins down his own talent as 'causing something slightly mad to happen. Viles Bodies was like that, completely barmy, enormously exhilarating, then it stopped being exhilarating and I gave it up. This is getting dangerously near that point but has been 10 times as exciting. The thrill is the discovery of talent. With the band I used to feel one was taking enormous trouble to provide excitement for 10 middle- aged men and a girl singer. This, if all's going well, is providing more excitement and educational, character- building stuff for an awful lot more people. But in the end it's deeply selfish. I am doing this as a writer. I want it to be taken seriously. I also want people to respond, to weep - bother the fact they are children.'

The lead of Mr Majeika is homegrown Mushy Pea veteran, Adam Davy, 15. Carpenter spotted Sasha Pick, 15, the star of Babes, at a local production of Guys and Dolls. 'I was nodding off when Sasha came on with that great number 'I love you a bushel and a peck'. I woke up. She is quite extraordinary - real star quality, natural vibrato.'

While Sasha laments Judy Garland's 'The Man That Got Away' and 'Night is Bitter', Carpenter will be fulfilling an old ambition, 'conducting from the pit, driving the show, laughing at the jokes. It's necessary for my sanity.

'The happiest moment of the entire company was when we were all coming back on the bus from Chipping Norton. There was a quite extraordinary feeling of euphoria, achievement, optimism which I suspect we'll taste again some time this week - then you don't have to explain why you're doing it at all.'

'Mr Majeika', matinees at 2.30; 'Babes', evenings at 7.30pm from 2-5 June, Shaw Theatre, 100 Euston Road, NW1 (071-388 1394)

(Photograph omitted)