The golden boy of pop-opera won't be his usual well-scrubbed self when he takes to the stage at Southampton's Mayflower Theatre for his musical theatre debut, starring as the man on the run in Tim Rice and Andrew Lloyd Webber's Whistle Down The Wind (March 1-6).

Former Chichester schoolboy Jonathan conquered the charts as a member of G4 a few years ago. He's since established himself as a major solo artist. Now he's tackling the musicals.

"I always want to keep myself under pressure, to give myself interesting new challenges", says Jonathan, a former student at Chichester's Bishop Luffa School.

"My recording career is on hold at the moment. This is full on in the show until the middle of August, and then I am hoping that I can get into a West End role or some more musicals later in the year. It's like taking a bit of a tangent in my career."
But not entirely new.

"The style of singing is something I have tried to incorporate in my career since I was young. I have always tried to sing musical theatre songs. I have always loved them and listened to them. I spoke to my agent and said I would like to do a musical. It came back that Whistle Down The Wind was a possibility and that (producer) Bill Kenwright was interested in seeing me to play the lead.

"I have trained to an extent in acting," says Jonathan who was brought up in Bognor Regis where both his parents were primary school teachers. "I was incorporating acting lessons in college, and I have also incorporated G&S shows through the years. Now this is more serious core acting. You have to think how to portray the character. It is daunting to be a character on stage with all the restraints and all the liberties that go with this and know that you have got to convincingly be this person."

In the show, in a twist of fate, the bright-eyed and youthful Swallow discovers a mysterious man (Jonathan) hiding in her family's barn. When she asks for his identity, the first words he utters are 'Jesus Christ'…and it's as though her prayers have been answered.

While the rest of the townspeople are searching for a fugitive escaped from jail, Swallow gathers the town's children who make a pact to protect their new-found saviour from the cruelties of the outside world.

Based on the landmark 60s film starring Hayley Mills and Alan Bates, the show features numerous multi-award-winning songs, including Boyzone's international smash hit No Matter What, which topped the UK charts for six weeks.

"The movie made the man out to be more scary and sinister", Jonathan says. "I am playing a more likeable character. Bill Kenwright likes the audience to feel endeared to everyone on stage in all of his shows, so I am a likeable villain!

"I am not sure if my character really killed someone or if he has been wrongfully accused. I have not quite decided, but I know that I am a good man that has just ended up in this situation. I am not sure that you have to be able to answer every question. You have to think about your character's life and where he came from, and I have definitely enjoyed analysing his whole character but you don't necessarily have to have all the answers."

More to the point is to show how powerful love can be when the innocence of childhood collides with the cynicism of the adult world: "It's about the naivety of childhood and their rapid acceptance that I am Jesus. And it is about redemption. It's just a really lovely simple story but it has got just enough complexities to appeal to adults as well as children."

And it's certainly fun working with the children on stage. They can be just a little volatile, with always the possibility that they will do the unexpected.

"One little girl started taking her shoes off. You've just got to work through it!"

Helping and also hindering the youngsters is the fact that they don't know who Jonathan is: "Their parents have told them that I am famous and they have got this weird conception of what that means. They see me on stage and they are a little bit freaked out. But it all adds to the characters that they are playing."

Jonathan, who offered one of the highlights of last year's Chichester Festivities with a memorable concert in Chichester Cathedral, married his sweetheart Debbie at the end of last summer.

"We got married in a slightly-bizarre location at the top of the Gherkin in London," Jonathan recalls. "It has got panoramic views which were wonderful. The backdrop for our ceremony was the whole of London. It was sensational, 40 floors up and looking out at the whole country, it seemed - looking out at where we met and where we live. It was an amazing experience."

Being married takes a little getting used to, Jonathan admits: "It was weird at first. I don't feel like I am old enough or mature enough to get married. It's real life! I am the first of my friends to get married, but it's a lovely thing.

"We'd lived together before getting married and people say 'What's the point in getting married', but it's very different - a huge difference. It's a wonderful feeling."

Jonathan's dramatic rise to fame came in the wake of three years of multi-million-selling success with G4, but it is his solo achievements that have sent his career into orbit. In February 2008, his first solo album, Tenor At The Movies, went straight to number one in the classical charts, hit top ten in the pop album charts, and made him the youngest-ever tenor to top the classical charts.

Tickets for Whistle Down The Wind are on sale from The Mayflower on 02380 711811 or online at mayflower.org.uk.