John Barrowman kicks off his high heels and peels off his stockings during a break from his West End role in La Cage Aux Folles, in which he stars as a drag queen.

“Dressing up as a woman is kind of liberating — I don't know what you women complain about, but the high heels are really painful,” he laughs.

This latest persona is a far cry from the the dashing, bisexual hero Captain Jack Harkness he portrayed in Doctor Who and the spin-off, Torchwood, but then Barrowman has never allowed himself to be pigeonholed.

He's starred in a succession of West End musicals, been a talent show judge with Andrew Lloyd Webber, skated in Dancing On Ice and hosted his own Saturday night show, Tonight’s The Night, on BBC One.

With his matinee idol looks, Barrowman, 42, exudes supreme confidence, yet it wasn’t so long ago he suffered horrendous panic attacks, he reveals in his memoir, I Am What I Am, following on from Anything Goes.

And the most recent attack was during his show at the New Theatre, Oxford, earlier this year.

“They started happening about 10 years ago. It started with anxiety and worked its way into panic. My sister gets them, my mum gets them. It doesn’t happen before a performance and is nothing to do with being nervous. Panic attacks come from nowhere.

“When they start to happen, you feel your left arm go numb and you think you’re going to die, or you’re having a heart attack. You think, ‘I can’t breathe, I’m sweating, my arm’s numb, I’m going to have a heart attack’. The adrenaline is pumping massively.

“Over the years, I’ve been on stage in the middle of a number and suffered a panic attack, been in the Tardis with the doctor and kept one at bay and, most recently, during my show in Oxford on my concert tour, I let one charge through my system while I sang on.

“I’ve been told that panic attacks are often triggered for no reason, but agoraphobia or, in my case, mild claustrophobia can be a catalyst. I very rarely get them now because I’ve learned how to cope with them.”

The attacks have obviously not affected his career. Today, he has so many offers, he has to turn down a lot of work — he’s just turned down a role in House, the hugely successful American medical series starring Hugh Laurie, and also said no to six Broadway shows last year.

He’s a multi-talented gay icon who’s devoted to his long-term partner, Scott Gill, an architect, and to his wider family.

His parents fly over to stay with him every three months at his homes in London or Wales, while his sister, Carole, helped him write the second volume of his memoir. Born in Glasgow, his family moved to America in 1976, when his father’s job for Caterpillar machinery company relocated.

He returned to England in 1990, taking his first professional West End lead as an unknown opposite Elaine Paige in Anything Goes. He has never looked back professionally, but Captain Jack was his big breakthrough.

“I was perfectly content to be working in the West End until I was in my early 70s and hopefully watching my career and roles change as I got older, then suddenly Doctor Who came along which took me in another direction.

“It’s changed my life in the sense that people offer me things now. Rather than auditioning, I can pick and choose.”

His run in La Cage finishes at the end of November before a stint in panto at Cardiff.

He then hopes to finish a new album to be released in the New Year. He’s currently in discussions about a second series of Tonight’s The Night and a fourth series of Torchwood.

“I won’t let people pigeonhole me,” he says, slipping on those agonisingly high heels again.

* I Am What I Am is published by Michael O’Mara at £20.