A 25-piece band strikes up in front of a rainbow-coloured curtain and suddenly there’s a rush and bustle of a genuine superstar on the West End stage – for one week at least. Idina Menzel’s back in town and, boy, does she mean business.

Much of her sound, I guess, is down to the size of her mouth and jaw, which she sticks on the audience with almost indecent glee. She explains why she’s more liberated when performing barefoot, and takes as much pleasure in her silver, black and gold silky chiffon gown as we do. Keeping her hair out of her eyes is a full-time job, too.

She’s not shy of making the obvious comparison with Barbra Streisand - actually, she’s a sort of gypsy, sexier Streisand - as she launches unapologetically into one of Streisand’s biggest hits, “Don’t Rain on My Parade” from Funny Girl; if she’s less precise and meticulous, she’s just as sassy and emotionally transparent.

I’ve seen her twice before: in Rent on Broadway and on the first night of Wicked in London. She honours both shows with fans’ favourites, even involving audience members in a song from the first show, and possibly getting more back than she bargained for.

“Without You” is given full value and perfectly articulated, but she does blur too many lines in Joni Mitchell’s great “Both Sides Now,” and even in the biggest number of all, “Defying Gravity” from Wicked. And too much of her chat is of the waffly unstructured variety favoured by American stars just thrilled and honoured to be here; sure, it’s a long trip from singing at Jewish weddings on Long Island, but so what?

She does a fantastic, unimaginable overlap of Cole Porter’s “Love For Sale” and Sting’s “Roxanne” and takes time to pay tribute to the late Marvin Hamlisch, performing the song from A Chorus Line, “At the Ballet,” that she sang at his memorial. I loved her a capello “Thank you” song and also a beautiful new item, “Learn to Live Without,” by the Next to Normal guys.

The noise is almost too much for the small stage, but Rob Mounsey’s musical direction, mixing a bunch of London musos (brass, strings, the lot) with her own tight band, is impeccable, and Menzel’s lung power seemingly inexhaustible. Above all, like all great singers, she palpably loves what she’s doing. And that’s half the secret.