Stephen Sondheim’s 1970 masterpiece was the first time I realised a musical could be about me. Its hero is Bobby, a New York man-about-town whose 35th birthday triggers a rush of anxiety that life may be full of parties and lovers but it lacks the comfort of company enjoyed — or should that be experienced — by all his married friends.

It was not that when I first saw the show in 1996 my life mirrored Bobby’s. We were both in our thirties, but I was already in the process of a separation that I knew would lead to divorce. Far from relishing the prospect of freedom, I was aware of a gathering loss. Still, where the show was — and is— a great comfort is the way in which it reflects all the conflicting pros and cons, ups and downs, hope and cynicism and love and loathing generated by being with other people, or as the climactic song sung by Bobby at the end of show, puts it, being alive.

The cast of that production, directed by Sam Mendes, was led by Adrian Lester, the first black actor to play the role of Bobby. For this one, directed by Marianne Elliott, the cast is led by the flame-haired Rosalie Craig, the first woman to play the role. And the effect here of swapping genders, which has become somewhat of a thing when reviving classics, especially Shakespeare, is that it reinvigorates a show which for all its brilliance had become dog-eared in its conception. For at the heart of Elliott’s show is the notion that it is just plain stupid to think that giving up freedom and lovers for a life of sex and marriage is a dilemma only for men.

Granted, a couple of New Yorkers in the audience complained that Bunnie Christie’s design, which sets most of the action in box-like apartments, meant they couldn’t see the city in which Sondheim sets his show. The cramped interiors bring to mind Hong Kong more than New York. But the rewards of turning Bobby into Bobbie are so bounteous that to focus on the set is to miss how George Furth’s witty book has been reenergised and modernised.

Bobbie’s air stewardess girl friend is now an air steward, played by Richard Fleeshman (cue the uplifting melancholy of Barcelona) whose Andy is as sweet and thick as clotted cream. And Amy, the neurotic Catholic fiancee to Jewish Paul, is now fiancé Jamie, superbly played by Jonathan Bailey who delivers the machine gun lyrics of Getting Married with the frazzled nervous energy of someone who has been shot with a taser.

He doesn’t see the point of marrying after living so long together. “Everyone will think I’m pregnant” he says. The line is funnier now than it has ever been.

Yet thankfully the gender of Joanne, whose view of relationships has been jaded by multiple marriages, has been left well alone. For if Joanne had become Joe we would have lost one of the best moments of a superb evening, when Broadway star Patti Lupone, swathed in fur and cynicism, sings The Ladies Who Lunch.