French and Saunders are calling time on their double act - and they’re doing it with all the energy, ingenuity and wonky editing skills that have marked out their 30 years together.

Half the time, this farewell West End show is pure pleasure. French and Saunders have never been an act with depth to them, but with surface like this, who needs it? They perform a doctor sketch on their white room set, displaying their debt to the gleefully warped logic of vaudeville: “As I expected,” Dr Saunders tells French, “you’re exactly your correct weight for your size.” French takes a chocolate detector into the stalls and finds, with the aid of video trickery, a rat in someone’s cleavage; Saunders dons a leotard to reprise her bulky Madonna impression. “You’re just too old for this!” French tells her. “I’m the same age as Madonna!” retorts Saunders, 50.

And are they too old for this? Well, they can certainly still perform the hell out of it - even Sex Talk, the first sketch they wrote together. With French giving ludicrously wrong sex advice to her fellow teenager Saunders, it’s as funny as anything they’ve done. Interacting as themselves, the poised, exasperated Saunders faces up to French’s exuberant innocent. And French in particular remains a phenomenally vital comic performer, whether boasting about " The Vicar of Dibley " (“I was the queen of Christmas!”) or playing a downbeat Saffy in the original " Absolutely Fabulous " sketch.

They’re still a terrific team. So it’s a shame that, after an irresistible first 40 minutes, we also see their dark side - their tendency to wibble on a bit, bantering way beyond the joke’s natural lifespan. A beautifully acted routine about two teens spending Christmas at boarding school makes an acute, bittersweet point - and then just keeps repeating it. A pre-recorded "Strictly Come Dancing " sequence goes on far too long before their old lady characters return to the stage to dance with mannequins of the show’s Anton du Beke and Brendon Cole. But only the sisters from Prickly Pear Farm and the expats from Biddeford, marvelling at how big everything is in America, are real duds.

“I banish you to UK Gold!” Saunders shouts, suspended in midair, at a dauntingly large vicar of Dibley doll. But she’s talking about the act, too. This fond farewell is part-fuelled by nostalgia - a " Thank You For The Music " finale offers both mock sentiment and actual sentiment - but French and Saunders’s force of personality can still propel their mix of character comedy, parody and banter. As ever, a lack of quality control keeps them good rather than great. But as they finish their time together by whipping out their willies - well, their fat men’s rubber willies - fans can rest assured that they’re leaving the stage with their indignity intact.

Box office: 0870 830 0200, to Nov 9

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