The heir to the throne has been skipping his fencing classes to pursue his love affair with an “unsuitable” fiancée. Who could be more unsuitable than a married woman? a prostitute? a transvestite? Jade Goody? No, it’s even worse than that: a Muslim.

In King of Hearts, a spasmodically funny farce about the royal family, Alistair Beaton proposes that while the monarch slips in and out of consciousness at Sandringham after falling off his horse, his elder son, Prince Richard, is secretly in love with Nasreen, a partly veiled Pakistani beauty who is the deputy director of an Islamic cultural centre.

While, in real life, we are told that there is not a shred of evidence to suggest that Princess Diana and Dodi Fayed were the victims of a murder plot, Beaton elaborates on the paranoia of Dodi’s father who still maintains that Prince Philip and MI6 planned the Paris car crash.

So, Beaton’s callous and craven Labour Prime Minister (Justin Salinger with a Jeffrey Archer-style jutting jaw) and his opposite number, Jeff Rawle’s Tory leader Stephen, conspire with the all-gas-and-gaiters Archbishop of Canterbury (Roddy Maude-Roxby) to reverse their decision to switch off the dying king’s life support machine.

Richard can be thwarted by a Royal Marriages Act which requires the king to approve the nightmare possibility of the liaison; how can we possibly have a Muslim in the royal family, asks the PM, if we plan to attack Iran?

Meanwhile, an officious little royal protection officer (hilariously pedantic Anthony O'Donnell) has exploded Nasreen’s luggage in a terrorist attack scare, and Richard’s younger brother, Arthur, has turned up roaring drunk in a rugby jersey.

The production by Ramin Gray and Max Stafford-Clark for Out of Joint is beautifully cast and extremely well directed. It makes the play look better than it is. For while Beaton’s royal fracas is a masterpiece next to last year’s downright embarrassing A Right Royal Farce by Toby Young and Lloyd Evans, it is still more of a cheeky, box-ticking satirical lampoon than a delirious theatrical concoction. Some of the humour panders too easily to liberal knee-jerk reactions and leaves a rather nasty taste behind.

The opposition leader is caught in flagrante with a homosexual apparatchik (Toby Dantzic) which ruins his suddenly hatched idea of running on a “party of love” ticket by approving the marriage. And as Nazreen’s offstage brother is framed in a growing criminal light, and the possibility of abdication grows stronger, the plot keels over and expires in a sustained rhyming doggerel epilogue.

As the two princes, newcomers Ben Righton and Christian Brassington carry uncanny physical resemblances to William and Harry, and are both extremely good. Zahra Ahmadi is a poised and persuasive Nasreen until Beaton’s plot reduces her to a cipher. Caroline Loncq is a scarily brutal prime ministerial aide. Old-style class and dignity is solely represented by Alister Cameron’s tall and suave loyal royal retainer.

- Michael Coveney