Her conversation is full of impressive neologisms (“when you have children you start to relativise everything”) and picturesque metaphors (“in the bucket”). She is a doting mother, passionate about her children, unable to be separated from them for long, and unsentimental about Louise Woodward, the nanny “She can fry, as far as I’m concerned That would be fine with me. If she killed the kid, I have no sympathy for her.”While her stage presence suggests a woman who has utterly drenched herself in the conventions of the Hollywood musicals, Ms Lemper will not admit to modelling her Velma on anybody. The rest of us might see bits of Ginger Rogers or even Joan Crawford on stage, but she.. “No, I’m not copying anyone Velma is my own invention I let her be a little brat. “We had the house, the school, I’d fixed up all my performances at supper clubs. Then this came up.” The family is now happily shacked up in Maida Vale, west London, and Ms Lemper, after two children and without recourse to gymnasia or ballet training for four years, found her leg muscles snapping back into place like steel ganglia.

It turned out they didn’t need the replacement – but two weeks later, I got a phone call saying they wanted me to open in London, but as Velma.”Lemper and her husband, David Tabatsky, an American actor and comedian, were then touring America with their children (Max, nearly four, and Stella, 15 months) and had resolved to move there from Paris. Then her agent called to ask if she wanted to audition for the part of Roxie, to replace Anne Reinking, the show’s choreographer “So I auditioned. I was getting just a little bit sick of myself,” she confesses in her beguiling Westphalia-goes-to-Hollywood accent. “I wanted to be in a theatre company again, to work together with people on stage, sharing the responsibility, playing one part.” She went to see Chicago in New York.

“Nobody in London knows that I’m a dancer, but everything I do is always with the consciousness of a dancer, the movement and sensibility.”After five years of singing “Falling in Love Again” and “Ich bin ein Vamp”, of reclining on pianos and swanning about in feather boas, she was ready for a change “I was looking forward to not always making my own show. She has taken her Blue Angel persona all over Europe and America, to rapturous receptions. So why go back to hoofing with cane and top hat?”Yeah, it’s another world,” she says wryly. “But it’s not a step back, I think, it’s a step in a different direction An excursion in a different musical genre.” She sighs. Although she has performed in musicals for years – she was discovered at 20 by Andrew Lloyd-Webber – she is more at home as a torch singer, embodying the spirit of Kurt Weill and the cabaret composers of the Weimar Republic, who were condemned by the Nazis as “degenerate”.

Her long face isn’t quite as Garboesque as expected, but her lustrous hazel eyes beneath the aqueduct-sized brows flash with spirit.The Velma in her soul has always competed with the Lotte, the Edith, the Marlene. I’m not 25 any more.”No, indeed, she is now a mature babe of 34, a seasoned chanteuse and transatlantic Euro-diva. Ms Lemper in the flesh, in her prosaic dressing room at the Adelphi with her cartons of Ribena and the noise of kango hammers for company, is thankfully less alarming than the man-eating Velma. Clad in a black T-shirt, a boucle sweater and white jeans, she is relaxed to a Zen-like degree, focused and forthright. You say, Oh shit, I hurt my foot or I tore a little bit of a muscle here, and this adds up when you do it eight times a week It really is very exhausting After two shows in a day, I fall into bed I can’t eat, I’m so tired.

When I come out on stage, I have to be so pow!pow!pow! And the adrenalin level is so high, you don’t even notice when you hurt yourself You notice afterwards, of course. You can always cover it up.”Feeling like someone interviewing a dervish about step-aerobics, I ask: Is it very demanding, physically? The vast McDonald’s-logo arches of Ms Lemper’s eyebrows spring an inch higher “It’s scary. It’s more like Greta Garbo has walked on to the stage of the Adelphi Theatre and proceeded to impersonate Josephine Baker’s debut at the Folies Bergere.”There are a couple of moments,” she admits coolly, “when I think, my God I’m going to lose my balance, with the high heels and everything? But I figure, when I get it wrong, I get it wrong, OK? When I saw the show on Broadway, with Bebe Neuwirth playing Velma, she’d done 150 performances and the night I saw her, she lost her balance and did a little hop But the audience didn’t know. You look at Ruthie Henshall, her co-star, and note how talented she is, how well she sings, what a dancer, what stage presence.