Up For Grabs, Wyndham's Theatre, London

This is, in many ways, the strangest experience in West End theatre since Jeffrey Archer tried to persuade us that he was the upright, wronged innocent in The Accused. There is almost that degree of discrepancy between the celebrity's public image and the stage role.

Madonna as an art dealer, I can buy. But Madonna as a desperately struggling dealer, still supported in her 40s by her husband? A Madonna with crippling debts who will have to debase herself by all manner of means to sell a Jackson Pollock or be forced to return to a humdrum job in marketing?

If there are going to be sex romps with giant dildoes, you expect Madonna to be calling the shots, not taking the orders. If there are going to be steamy lesbian snogs, you expect her to initiate them rather than politely endure them. But in David Williamson's Up for Grabs directed by Laurence Boswell, it's a bogus "I'm a good girl really'' Madonna that's on offer.

The first night audience cheered her to the chandeliers before she'd uttered a word. She certainly looked gorgeous standing alone on stage in her white mini-trench coat and supposedly gazing in pure appreciation at the pictures in the New York Met.

If she had held that pose for a while and then let people go home, some of us would have been a whole lot happier. Her role as Loren requires her to power the comedy forward with lots of confidential chat to the audience about the scrapes and indignities of sustaining a bidding war. But she is too stiff and untrusting to create the requisite rapport.

In her scenes with Boswell's vivid supporting cast (in which Sian Thomas is outstanding), Madonna is so busy concentrating on rehearsed effects that she fails to create any sense of spontaneous connection. On occasion, you feel that the car in Chitty Chitty Bang Bang acts less mechanically.

This central casting is an example of grandiose ideas backfiring farcically. It's like the fate of Kel (Daniel Mino), the hip young dotcom "millionaire'', who is one of her potential buyers. Not content with his merely large penis, he has undergone the surgery to make it a whopper. The trouble is that the resulting member is so large that it curls round in a useless doughnut ring.

You wonder if the Australian dramatist, David Williamson, has struck any analogies. Merely a box-office smash last year in Sydney, the play has now taken a mega-star on board, had a Manhattan makeover on her behalf, and as a result had its message badly distorted. I mean, how can you mount even a soft-centred satire about the inflationary commercialism of the art market and give the leading role to a "material girl'' and global celebrity whose simple presence turns the event into a frenzied circus of hype, with tickets exchanging hands for £500? Mr Williamson should write a rueful comedy about the experience. It could open in the West End and star Madonna's best buddy, Gwyneth Paltrow.