Sitting in her dressing room while putting on her make-up, she looks as glamorous as Roxie and Velma dream of being in Kander and Ebb's long-running musical about crime and celebrity,Chicago.

We're in the middle of a heatwave. How does that affect the action on stage? "This being Britain, the theatres aren't air-conditioned, of course, so we're all drenched in sweat by the end of the show — and so is the stage floor, which can make it very slippery. The trouble with a heatwave is the effect not on the cast but the audience. Heat induces lethargy, which as a performer you have to shrug off as you as you step on stage, but when you do so, you can sense the audience being rather sleepy and so you have to work that much harder to get the energy levels going."

I saw the show last week, and the energy levels seem as amazingly high as when it was first performed, back in 1997. "I think so, too. The producers have been very adept at constantly changing the cast, which keeps the show fresh, as you have a frequent supply of new blood, of people who are hungry for success — which is part of what Chicago is all about."

You've had a baby girl . . . playing Velma's a challenge at the best of times, but it must have been even more so after having a baby?"Yes, but I knew I wanted to get back to work. I had six weeks rest and then gradually began exercising and getting into shape again. "The trouble, for a dancer, with having a baby is that you put on a lot of weight, and when the baby comes out and this huge bump goes down, you find that a lot of other weight — and expansion — stays. I'd gained two stone! So I had to get fit and in shape with this extra two stone to sweat off. I knew it would be hard work, and I'm used to that, the issue really was that it was frightening to have to get back in shape so soon."

While you were still pregnant, you gave a master class on music theatre at the Theatre Royal, Haymarket, which I saw. You're obviously very good with students. Is this something you have a lot of experience of? "Yes, I've done it at a number of venues, like the Actors' Centre and Guildford School of Acting. . . . I think it's important to give something back to this profession, and when I teach, I do so without a fee as it's my way of giving something back.

"It's helpful for the students to have a class or classes not just from teachers, however good they may be, but from someone who was a student like them and has actually gone out there and made it in a fairly tough, competitive world, and can bring that experience back with them and pass it on."

Once your contract runs out at the Adelphi in September, what other plans have you got? "I'm sticking to Bob Fosse's choreography, and appearing in Fosse at Edinburgh and in Manchester. I love Fosse's work.

Work is the operative word with his choreography, isn't it? "Yes, but it's a lot harder here in Chicago than it will be for me in Fosse where I'll have two dance numbers and four or so songs to sing."

Will you be doing anything else in London before heading North? "I'll be singing in the last night of the Proms in The Park, which I'm looking forward to, though I haven't decided which songs I'll be doing yet. Performing in the park will be magical, and I'm glad to see London using its parks more: One of the great pleasures I had when living and performing in New York for two years was the way everyone took a blanket and picnic to Central Park, and enjoyed the many concerts and shows they do there every summer. I'm glad we're catching on to the idea!"