Moonfleece, Rich Mix, London

Jerry Springer the Opera famously inflamed Christians to most un-Christian thoughts of censorship and worse. Cat-calling protesters marched with placards outside the fringe theatre that hosted the London premiere of Corpus Christi, the Terrence McNally play that dared to suggest that the God of love might just as well have been gay as straight or sexless. Not, though, that Christians have the monopoly on illiberal outrage. Some members of the Sikh community were so affronted by the play Behzti at the Birmingham Rep that violence broke out among a minority of the protesters and performances of the play were cancelled two days later.

But the reaction to Moonfleece – the splendid Philip Ridley play that now receives its professional premiere in David Mercatali's brilliantly alert and magically tragicomic production in Bethnal Green's new Rich Mix arts centre – seems to be of a different order of revealing negativity. Originally developed a couple of years ago with sixth formers as part of the National Theatre's invaluable New Connections season, the play – in true Ridley-esque East End Gothic fashion – takes a darkly fantastical but psychologically acute look at the emotional origins of BNP activism in one Bethnal Green family. It's as if a lurid political rosette were to be traced back to its poisoned roots.

Pointedly mounted as we are about to go into a general election, the play had flushed out the BNP in its true colours even before its opening night. The organisation has refused all invitations to share a public platform to debate the issues raised by Moonfleece, while not being shy of posting unedifying comments about it on theatre websites. The level of the attacks there is summed up by the suggestion that it constitutes an insult to the indigenous white population and that a better play would explore the downside of multiculturalism – the "Muslim paedophiles" who groom young girls and the "Somali drug dealers" who kill young males. To which the democratic answer is: fine, why not write or commission such a play?

Set in an abandoned East End council flat, this play opens like an amphetamine-fuelled droll cross between Pinter and the (Ridley-scripted) Kray brothers film. Spruce in identical grey suits, red ties and badges, three twentysomething brothers, surnamed Avalon, descend on the mixed-race teenager who is squatting there. One of the brothers is eye-poppingly thick; the other two are variously troubled. All of them are racists and fascists.

In one sense, you could say that Moonfleece is semi-autobiographical. It's as if Ridley, who, as a child had to look after his own highly phobic brother when his mother fell ill with depression, has hypothesised an alternative past in which the family became the prey of a white racist stepfather who himself had family reasons, though not justifications, for his prejudices. The sibling bond is very powerful in Ridley's plays and revelation of the way that it was betrayed here causes the climactic moment of self-discovery and potential change.

To 13 March (020 7613 7498)