DID you ever suspect a villain of the deepest dye lurked beneath the squeaky clean matinée idol looks and the retina-searingly white teeth of John Barrowman?

If so, then his silky-smooth transition to brutal psychopath in Desperate Housewives won’t have come as a surprise.

The song and dance man (“entertainer with a capital E” as his website has it) played charismatic killer Patrick Logan in the American television juggernaut earlier this year.

“What’s funny is that people keep asking if it was hard to play a bad guy, and I have to be honest and say I found it really easy,” he cackles.

“All I really did was tone everything down to be the bad guy!”

Barrowman tells a story – complete with what, by his own admission, is a “terrible Russian accent” – about a recent holiday in the Lake District when he was approached by foreign tourists who instantly recognised him as the rotter from television’s Wisteria Lane. It’s yet another step in a different, altogether more international direction for the Glasgow-born, American-raised performer.

There are plenty who bewail the perils of fame and the artist’s misery at not being taken seriously for one’s craft, but Barrowman has a refreshingly uncomplicated relationship with success and adoration – he loves it, and doesn’t care who knows it.

Earlier on in his career, he was told not to take a role in pantomime, but instead took the advice of musical theatre veteran Elaine Paige to do what he wanted to do.

“People said: ‘Oh, you don’t want to do panto, dear – that’s another rung down on the ladder.’ I just thought they were snobs. I wanted to work, to have a home and a nice car and to do that maybe I’d have to do panto or commercials or whatever – I never restricted myself.”

Knowing on which side his bread is buttered has served Barrowman rather well; it’s doubtful his more precious counterparts could’ve made the transition from musical theatre to “omnisexual” science-fiction hero Captain Jack Harkness, by way of a recording career that has shifted more than four million albums.

On Friday he’ll appear at the Pavilion Theatre in Bournemouth with a big band in tow to perform songs from his latest, self-titled album. But the Barrowman battlebus isn’t exclusively made up of muso types.

“I take my family with me – my mum and dad come over and they travel around on tour with us, which is great. My partner Scott (Gill, an architect, whom Barrowman met at the Chichester Festival Theatre) has his own company that he runs, so he comes to some venues too. When we’re in Glasgow, I have a bit of a do after the concert which allows my mum and dad to catch up with friends and family there.”

Bless him! Small wonder he’s so beloved of old ladies across the nation. But Barrowman’s appeal is never quite as sharp in its focus as to be purely about the mum demographic.

This week, his performance will be seen by people who’ve followed him from his musical days, maybe a few from his tenure on children’s TV and the most recent additions in the Torchwood fans.

Barrowman’s performance as interstellar agent Captain Jack in The Doctor Who spin-off has propelled the programme to ever greater heights. Its success on the BBC America channel means the next series will be co-produced by US production company Starz.

Fans had worried that an American influence might see the show’s adult themes cleaned up, but if the company’s Spartacus: Blood And Sand – with its blue language and sexual content – is anything to go by, they have nothing to worry about.

“It’s an amazing thing for the show,” Barrowman explains.

“It means we can keep the truth of the stories and the characters in Torchwood and still have the edgy storylines, as well as it being a great ambassador for the United Kingdom. I’m exceptionally proud it’s become international.”

For all his all-American charm and knack for saying just the right things, Barrowman can also be quite a candid interviewee. He’s more than capable of laughing at himself (perhaps that bit easier for someone who, at 43, is a little beyond the earnest precocity of youth) and makes no bones about dying his hair and treating himself to a spot of Botox from time to time.

He is also straightforward about his rumoured involvement in Glee, the US television smash hit schlock-fest that follows the trials and tribulations of a high school singing club. He’s the perfect fit for the unashamedly garish world of McKinley High School.

“The fact of the story is that I’m in a fortunate place in my career where if I ring up a casting person and say I’d like to come in and discuss some possibilities, it happens. And that really was it – there was no audition or time scale, they just said they’d see what was coming up. But I don’t worry about things like that. You do what you think is right and if it happens, it happens.”

The success of Glee is not a million miles from the search-for-a-star shows in which Barrowman has appeared as a judge. Andrew Lloyd-Webber’s How Do You Solve A Problem Like Maria? and Any Dream Will Do have had their detractors, but Barrowman, a close friend of the musical theatre colossus, says they’ve put bums on theatre seats.

“They’ve put musicals into a different realm with the public, which is something I’ve always believed in. When I was asked to do those programmes I said yes at the drop of a hat. I think everybody loves the escapism of them all.”

It was in musical theatre, of course, that Barrowman made his name (his CV includes Miss Saigon, Phantom Of The Opera, Godspell and Sunset Boulevard), but his early forays into television weren’t without their complications – he was advised against being open about his sexuality. Curiously enough, he would be turned down for the role of Will in Will And Grace later in his career for being “too straight”.

As a modern veteran of showbusiness in almost every conceivable incarnation, what would his advice be to young, gay performers?

“I wouldn’t hide anything, I wouldn’t lie about anything… be yourself, and if someone asks you a question, either answer it truthfully, or tell them it’s none of their business.

“I still get ‘gay actor’… do you say ‘hetero actor’? Why do we need to label things like that? But the important thing is not to lie, because then people have a right to dig.”