On Your Toes, Royal Festival Hall, London

Tap, smoulder, jump - it's the lean, mean dancing machine

David Mamet, who needs him? Almost 60 years before the teacher-pupil sex allegations of Oleanna, Richard Rodgers and Lorenz Hart had Professor "Junior" Dolan making love to student songwriter Frankie in On Your Toes. OK, it isn't exactly "Paedophile Theatre Scandal!" We are, after all, in the innocent days of the Thirties Broadway musical.

That said, sex is undeniably in the air. Only minutes into the plot, Anna-Jane Casey's lovely Frankie steals unexpectedly back into the schoolroom and discovers her professor leaping and tapping to his heart's content. "You're a dancer," she gasps, "a real dancer!" Frankly, Frankie's not the only one experiencing a thrill. A tiny jolt of pleasure surges through the entire audience because the smoulderingly lithe and blithe man in question is Adam Cooper.

Best known as the sex-drenched star of Matthew Bourne's Swan Lake, Cooper not only proves to be as good a tapper as he is a ballet dancer, he's also revealed as being no slouch in the choreography department. And boy is that crucial. This 1936 show is revolutionary.

You only have to glance at the Busby Berkeley movie musicals of the period to know that until this, most musicals weren't properly dramatic. Nobody cared about plot, they just lapped up sketchy love stories designed solely to support the charms of leggy showgirls. But On Your Toes is the high-spirited tale of a secret-ex-vaudeville-hoofer-turned- music-teacher who collides with the Russian ballet. A love of dance will out, and our love-torn hero winds up cavorting through a deliciously overdressed cod-classical ballet and, better yet, stars in the "modern" ballet Slaughter on Tenth Avenue as the hoofer who messes with a dancer and a gangster in a downtown dive. In one lovely leap, Rodgers and Hart cunningly wove dance into the heart of their structure. Which is why George Balanchine agreed to choreograph the original production.

His are giant footsteps in which to follow but, happily, Cooper is undaunted. His solo and duet work is as dashing and dramatic as you expect. He's also good at injecting fizz into the company numbers. But he's not fully-fledged yet. Take the title number where the students' riotous tap routines meet the show-off splendour of the ballet company literally up on their toes. Great choreographers can raise temperatures and pulses, but Cooper doesn't quite manage to build energy to boiling point. The number doesn't climax, it just stops.

Part of his problem is the venue. The Festival Hall is far better suited to concerts than theatre. This material needs stronger framing and focus. Designer Paul Farnsworth cunningly surrounds the action with moveable blue walls. But for all the fuschia lusciousness of Chris Ellis's lighting, the vast stage dwarfs the comedy and overplaying by certain cast members doesn't make it any funnier. Worse, at the final preview I saw, Paul Kerryson's staging of the climactic murder plot was fudged and weak.

On the plus side, Irek Mukhamedov can still induce collective jaw-dropping by vaulting across the stage. And Sarah Wildor is clearly having a ball with both the ludicrous accent and attitude of over-the-top ballerina Vera Baronova - and her pas de deux with Cooper are ravishing. And then, of course, there's the score. The wistful love duet "There's a Small Hotel" is a little miracle of songwriting: the moment where the yearning, musically rootless verse slips effortlessly into the chorus and into the home key should be like the sun suddenly coming out. But conductor Julian Kelly's inflexible style buries the moment. He does, however, encourage terrific playing from the 23-strong band.

Dance in musicals reached its apogee in 1975 with Chorus Line and Chicago. After that, with few exceptions, it upped and died. Seeing the fun in On Your Toes, even in a flawed production, is a zinger of a wake-up call.

Royal Festival Hall, London SE1 (020 7960 4242) to 6 Sept