Theatre:THE RIGHT SIZE PURCELL ROOM, SOUTH BANK

About half way through Tuesday night's performance of Hold Me Down, a woman sitting near the front got up and left. It was an action so perfectly awkwardly executed (she waved apologetically at those on stage) that for a moment you were almost convinced that she had been planted there by the Right Size.

A short while and a few rows back, company-member Micheline Vandepoel had stood up in a shabby mac, complained about harrassment of the audience and, without warning, shot Mr Wainwright, Sean Foley's convincingly hapless audience volunteer, stuck on stage for theree weeks with a useless magician (Hamish McColl) and desperate to escape.

Perhaps the departing woman had a horrible premonition that the show was going to explore the audience's relation to theatre using front-row victims and wasn't standing - or sitting - for it. Whatever the reason, her early getaway drew attention to the central strength - and weakness - of the Right Size's latest piece. While McColl and Foley's immaculate, often hilarious slapstick double-act taps into our deep- rooted yearnings for vaudeville, the audience-directed dialogue implies a significance that never surfaces. Much of the best material is at the beginning - business with a fake catapult, dummy legs, abortive anecdotes and delayed lip-synching. Much is at the crowd's expense: McColl ripping up the programme shouting"Fools. You believed this? Nothing up here is believable."

Thereafter, with the appearance of a mute, more successful magician, Old Timer (Vandepoel again), the Beckettian overtones become laboured. Exchanges like "Don't be fooled!" / "We've been fooled!" and the useless ladder that descends from aloft could have come straight out of Brodie's Notes Godot. That director Jozef Houben never allows the now stock-in- trade physical pace to slacken is one thing. But it's only during moments illustrative of Houben's association with Theatre de Complicite - the powerful visual transformations in which Vandepoel unfolds a blanket-sized newspaper and turns into a mountain, say, or Foley stamps the ground, imagining he's a horse - that the piece really disproves its self-appointed "shallow and happy" tag.

n To Sat (Booking: 0171-928 8800)