He was born Mark McLachlan and grew up in Clydebank where, aged 17, he formed a band with three schoolmates.

They called themselves Vortex Motion - well, it was the Eighties - and later changed it to the more radio-friendly Wet Wet Wet.

Mark also changed his name, to Marti Pellow, and became a twinkly-eyed pop pin-up whose trademark grin and cheeky charm melted the hearts of teenage girls, mums and nans.

A quarter of a century or so later, Marti has undergone another metamorphosis, into a musical theatre leading man. The twinkly-eyed charm is still there, but for his current role he’s tapping into his dark side.

Marti has taken on the dual roles of Dr Jekyll and Mr Hyde in a musical adaptation of Robert Louis Stevenson’s gothic novella, which comes to Bradford next month.

Billed as “glamorous, sexy and deliciously wicked”, the show is about brilliant but obsessive scientist Dr Jekyll, whose sadistic alter ego wreaks havoc across Victorian London.

“It’s a gothic masterpiece, a story everyone’s grown up with, and there’s a misconception that it’s about a man who turns into a monster – but it’s so much more than that,” says Marti.

“Jekyll is a complex guy. He becomes obsessed with the idea that man is both good and evil, and attempts to separate the two. It takes over his life, everything else goes on the back burner.

“I’ve got to make him accessible and embrace his plight, so the audience feels for him. Hyde takes care of himself, he’s on a mission to cause chaos.”

Marti, 46, says the story lends itself to a musical interpretation. “I explore each character and their inner selves through song,” he says.

“It’s a beautifully-written score; you can’t go wrong with the lyrical prowess of Leslie Bricusse, unleashing all that inner turmoil.”

It’s quite a physical role, something Marti has embraced since he took his first steps into musical theatre.

“I hadn’t expected it to happen. I did a concert at the Royal Albert Hall, and Ruthie Henshall, who was there, encouraged me to do a musical. Then I was asked to play Billy Flynn in Chicago,” says Marti. “It gave me a taste for it. It’s good to have several irons in the fire, you know?

“It’s about embracing life’s challenges, keeping it colourful. My father was a labourer and earned his living digging in all weathers. If that was the reality, I wanted the make-believe.”

After Chicago, Marti played devilish charmer Darryl Van Horne in The Witches Of Eastwick.

Wet Wet Wet were one of the most successful British groups of the Eighties, selling more than three million copies of their debut album. The hits included Goodnight Girl, Sweet Little Mystery and Love Is All Around, their version of the Troggs song which got the ‘Wets’ into the record books when it reached No.1 in 15 countries, topping the UK charts for 15 weeks in 1994.

The band came across as cheeky popstrels, but Marti says they wanted more than a brief stab at fame. “We had youth on our side and we had a laugh, but we were conscious of longevity,” he says. “We soon learned about the power of music – they may have been just three-and-a-half minute songs to us but they became the soundtrack to people’s lives.” He continues to perform with Wet Wet Wet – they split in the late 1990s and later re-formed after the boys supported Marti at his mother’s funeral – and as a solo singer.

Marti’s platinum-selling debut solo album, Smile, was followed by Top Ten singles Close To You and I’ve Been Around The World.

“We started out doing Clash covers in pubs, now I’m working with some of the finest jazz and soul musicians around. I think you grow into music – there are some lyrics you can only get away with if you’ve lived a little,” he says.

There goes that twinkle in his eye again.

* Jekyll And Hyde runs at the Alhambra from April 11 to 16. For tickets, ring (01274) 432000.