The unsung hero who really knows the score

Out of the spotlights, it's the West End music directors who keep the hit shows on the road. Edward Seckerson talks to 'Kiss Me Kate's Gareth Valentine

More often than not it's only the backs of their heads that you see, just visible over the rail of the orchestra pit. They don't make an entrance like their elevated colleagues at the opera. There's no bow, no round of applause. No acknowledgement at all. A brief telephone conversation confirms that the band is all present and correct, that the house is seated, beginners are in place, and the show is go. Overture, maestro, please.

So much for the "glamorous" life of a West End or Broadway music director. The cursory bow at the end of the show is all well and good, but who's looking at the smiling face peering over the parapet when the applause is going literally overhead to those who traditionally bask in it: the stars of the show, the actors and singers who win the Tony and Olivier awards. There is no such recognition for "the best music direction in a musical". Stage direction, choreography, design, orchestration (finally), yes, but music direction... no.

Are changes afoot? Has the call finally gone out: music directors of the world unite, your time has come? Visibility has certainly risen; on Broadway right now the well-toned bare back of the female MD on The Full Monty is vigorously engaged in a kind of aerobic workout for every show, disco-dancing her way through the score. In 42nd Street the MD rises up from the pit like Reginald Dixon without his mighty Wurlitzer, while in Urinetown he is silently escorted to his keyboard by armed guards. It's a full couple of minutes before you realise he's not a character in the show.

In Chicago, the MD is very much a character in the show. He even has dialogue. The West End music director Gareth Valentine spent two-and-a-half years making real with the words "and all that jazz" from the stage of the Adelphi Theatre, London. For he and his band it was a little like being on parole, out of the pit and into the limelight. A long run for good behaviour.

So what's the life of an MD really like? What does it actually entail? Turning up at the theatre every night to conduct the show is part of it, a big part. But, as Valentine explains: "It's a little like thinking that vicars only work on Sundays." Once running, a major musical loses all its prime movers and shakers. The director, choreographer and musical supervisor will for the most part disappear, leaving the resident director and music director in charge of day-to-day maintenance. There's recasting to consider, understudies and second covers to rehearse, a band to keep in shape, quality control to supervise, egos to massage. Your leading lady may feel off colour, insecure, unloved. With no director around, who's the therapist now?

Gareth Valentine is doing the business in London for Michael Blakemore's hit revival of Cole Porter's Kiss Me Kate, fresh from Broadway. We meet backstage after the third preview, a matinée. Not everything about the show has quite gelled to Valentine's satisfaction, but right now he is thinking pizza and a quiet chat with me.

But the short walk from his dressing room to the stage door is much longer during previews. A key member of the cast collars him. "How was it for you, darling?" – or words to that effect. "Not great," he replies candidly, unwittingly awakening the spectre of thespian insecurity. There follows what would seem to be a pre-emptive strike from the lady in question. Could he possibly "goose" her big number a little by picking up the tempo? Of course, darling. Absolutely, darling.

Valentine is far better at the psychology than he chooses to admit. There's a performer's instinct about him. Indeed, he had planned to be a singer. Not a show singer, mind, but an opera singer, a lyric tenor. He was promising as a boy treble, highly commended at eisteddfods in his native Wales. Once at the Royal College of Music in London, singing and piano were joint studies. Masterclasses with Sir Peter Pears at Aldeburgh (after Benjamin Britten's death) led to a private arrangement back in London; Valentine would play piano for Pears in return for singing lessons.

But he ended up playing far more than he sang. He became a répétiteur at the London Opera School and taught when he could, subsidising his income by playing at the gay nightclub Heaven on Equity nights. There he was spotted by an associate of Anthony Bowles, then MD on Andrew Lloyd Webber's hit shows. Valentine was a prime prospect.

His first assignment – a show called Take Eight at the Royal Exchange in Manchester – was a flop, but thereafter (with the notable exception of The Baker's Wife) it was pretty well hits all the way. He's struck up a particularly close relationship with the songwriting team of John Kander and Fred Ebb (Cabaret, Chicago and Kiss of the Spider Woman) and his successes at the Donmar Warehouse in London – most recently the revival of Sondheim's Merrily We Roll Along – have showcased his extraordinary keyboard skills, the driving force behind most of the brilliant orchestral reductions deployed there.

Having perfect pitch certainly helps, but Valentine can hear something once and instantly reproduce it with all the harmonies intact. Band musicians respect that, and he works with the very best. Standards, he says, have "gone through the roof in the last 20 years". Some of the finest musicians he has ever encountered play in pit bands. Their versatility, he says, is staggering. In a Sondheim show they'll know that absolute, crystalline precision is everything. In Kiss Me Kate they'll straddle the schmaltzy Viennese operetta style of "Wunderbar" and the swing jazz epitomised in a number such as "Too Darn Hot". And they'll do so instinctively.

What they want from their MD is clarity of intent; a beat they can follow, every tenuto or ritardando of every phrase precisely signalled. Orchestra pits are cramped, sightlines to the conductor are awkward. Sound bafflers come between you and your colleagues, you can't hear them, you can't see the stage. Never mind parole, this is solitary confinement. But the music goes round and round and comes out sounding swell. It's an unseen miracle.

One of the biggest challenges facing any MD on a long run is the question of maintenance, keeping the show fresh while not compromising its consistency. Valentine doesn't believe in turning long-running shows into clone zones. It's well known, for instance, that the Disney corporation strives for laser-print copies of all its shows wherever and whenever they play. This is not Valentine's way. He believes in a degree of creative freedom within a practised framework. He wants his performers to continue unlocking the songs. Very often it's the tiniest nuances that make the biggest difference. The audience should feel it too, without quite knowing why.

Valentine is a colourful character, in every sense. His body is not so much a temple as a gallery. Check out the V&A museum's website (the calendar, too; October, he thinks) and you'll see why. From the neck down he's artwork. Tattoos. A walking exhibit. Not quite what one might expect from a chap who's just completed a year's sabbatical studying theology. But then Valentine is a mass of surprises, his newly-recorded Requiem being one of them. He composed the piece in 1993 in memory of all those who had died of Aids. As a gay Christian it seemed only fitting that his first major composition should be a requiem mass. No compromise there. His partner of seven years, Michael, died shortly after the first performance.

Now Requiem has been recorded, and sales from its release on World Aids Day (1 December) will benefit the cause. It's a lovable and loving piece, which not surprisingly brings a touch of "musical theatre" to the liturgy, lightening the Old Testament tone to an almost insouciant melodic sweetness. A choirboy skips through the "Recordare" as if the judgement book were a school register; the "Lacrymosa" brings a hint of British Airways ads with its Delibes-like harmony; and the gorgeous big-hearted tune for the "Offertorio" is the healing benediction. It's as if all the halos have been picked out in moving lights.

Valentine will like that image. He's big on irony. He once contributed a song about the serial killer Dennis Nilsen to a benefit for the fundraising group Crusaid. Like I say, a mass of surprises.