Billy Elliot The Musical, based upon Stephen Daldry's classic movie, is just irresistible. It catches you - or at least me - in its fervent grasp, and pins you down with all the artfulness of a vintage seducer, right to the misguided, sentimental finale.

At that lachrymose moment Billy's dead but smartly dressed Mammy appears from the wings and sings "In everything you do always be yourself." to the quavering string accompaniment of Elton John's beguiling music. You can almost feel the massed drip of the audience's tears.

That familiar struggle to be true to your self, against hard odds and harder knocks, motivates young Billy Elliot, the would-be ballet dancer played to the manner born last night by the sensational 12-year-old Royal Ballet student Liam Mower, and gives this musical its passion and poignancy.

More, though, is at stake than Billy's eagerness to dance. This is an evening which throws a fierce political punch as well as an emotional one. No modern musical has struck such rebellious, old Labour, workingclass conscious notes.

Lee Hall, whose book and ardent though feeble lyrics borrow much from his Billy Elliot film script, sets the musical in 1984 when miners were out on furious strike against Mrs Thatcher's pitclosure programme.

He juxtaposes the miners' selfless solidarity, which ends in defeat, with Billy, the individualist, in his ultimately triumphant battle to convince his prejudiced father and brother that ballet dancing is not just for "poofs".

Stephen Daldry, always at his best on the grand scale, deftly marshals a throbbing mixture of angry miners, threatening policemen and little girls in tutus - all singing. Ian MacNeil's versatile designs set the changing scenes.

Hall's songs hark back to old working-class culture. A musichall, Christmas pantomime song, with masked impersonators of Mrs Thatcher in accompaniment, recalls Joan Littlewood's style but indulges in crude political name-calling. Hall's banal song The Stars Look Down, a malevoice, defiant miners' chorus, is rendered poignant by John's impassioned accompaniment.

His music, in fact, whether for solo ballads or choruses, achieves his old lyrical dynamism. The sequence in which Billy and his transvestite, not quite prepubescent friend dress up in drag and dance is not just endearingly comic, it is fortified by John's lilting accompaniment.

Too much time, however, is spent on politically motivated vituperation and the miners' lamentations, not enough on Billy's battle to become a dancer. The evening's prime attraction, Liam Mower in the title role, casts a long spell.

Haydn Gwynne makes a fine characterisation of the sparky Mrs Wilkinson, that bored defiant teacher of ballet steps to girls. She sees more than a flash of potential in Billy whose father, a far too old Tim Healy, hates the whole dancing idea and tries to sabotage his determined son.

Mower dazzles in a sequence of dance numbers, spinning and twirling like an electric top when auditioning before the snooty Royal Ballet judges, engaging in spectacular gymnastics, from breathtaking aerial somersaults to remarkable bodily contortions that defy description

Mower's voice is nothing to rave about, but he makes the evening marvellous with this dancing display. There is nothing more glorious on the London stage than Billy's dream sequence in which he and his older self (superb Isaac James) dance together in feats of soaring virtuosity.

Billy Elliot the musical is not as welldeveloped or resolved as Billy Elliot the movie. Yet when Mower reveals a strength that belies his slight frame this musical conveys a raw excitement no film can match.