Ball, one of the West End's highest-paid stars, plays a middle-aged American woman in the musical, and wears a fat suit, wig and flamboyant clothes for the part.

A source said that a number of fans failed to spot him in the preview shows and demanded a refund.

A source said a number of Ball fans failed to spot him in the preview shows of the Broadway hit.

Producer Adam Spiegel denied the refund claim, but admitted several members of the audience had complained about Ball's apparent absence from the show, which has its opening night at the Shaftesbury Theatre in London tomorrow.

Spiegel said: "We have had a dozen complaints to the box office staff at the intervals during the previews.

"Michael is extremely flattered that his disguise is so good. He does make an extremely impressive woman."

Ball, one of the West End's highest-paid stars, disappears for the entire show into the persona of an enormously overweight, agoraphobic, middle-aged, American "trailer trash" mother called Edna Turnblad.

The transformation into Edna Turnblad, which the star insists on doing himself takes Ball 40 minutes.

The 45-year old performer has to wear a fat suit into which he slips a pair of plastic size 46EEE breasts. Weighing 2lbs each, the singer has been complaining that they have given him bad back pain, according to Spiegel.

Ball's makeover is completed with support tights, painting in the shadow for a cleavage, waxing out his eyebrows, a choice of half-dozen wigs and dresses, false eyelashes, layer upon layer of foundation to hide his stubble, make-up, and a weekly shaving of the chest.

The show's manager Rebecca Quigley said: "Michael says that he thinks that all men want to dress up as a woman once in their lives. He says that this is his moment at last – and he's loving it. He has confused a lot of people.