It would be easy to assume Keith Jack’s shiny black head has been turned a few notches in recent years now he has gone from shelf stacker to making a living out of using his voice.

Since his appearance on Any Dream Will Do, the BBC reality TV show, he has been able to leave his old job behind his job and this month will be on stage in Glasgow playing the lead in Joseph And The Amazing Technicolour Dreamcoat.

Just last night the 21-year-old Edinburgh-born musical theatre star was on stage in Birmingham, in the title role, and holding each of the 2,000 fans in the palm of his hand.

Since losing out to Lee Mead in the BBC show Keith has appeared as the Narrator in the musical of the Biblical tale and released two solo albums.

He also sang on John Barrowman’s album and in the musical Only The Brave.

Keith reveals he is set to treat himself to a new car, but when he tells you what he is looking for it gives a real indication that the former Tesco worker’s head is in a fairly fixed position for one so young.

“No, it won’t be an Aston Martin, or a Bentley Convertible,” he says, grinning, when it is suggested he may source the sort of car favoured by footballers.

“The truth is, I’m quite tight with money and don’t like to spend it. And with insurance what it is these days it will be more like a Fiesta, or maybe even a Golf. Why would I need anything else?”

Why indeed? Keith Jack certainly seems entirely unaffected by his success.

“I think I am,” he says. “I love what I am doing and am really appreciative of all I have. After all, how many jobs are there where you get applauded for what you do every day? And if you have the right friends around you then they keep you right.

“You just can’t lose the plot in this business. I’m sure if you are not nice to people it will backfire on you.”

In a business where egos are bigger than the cost of a London West End show on a Saturday night those are wise words from one so young.

But even from boyhood Keith always fancied himself to be a singer.

“I did dream about it,” he says. “I had this thought in my head I’d love to play Joseph or Phantom, but then I have always wanted to sing.

“The neighbours told me I used to sing myself to sleep at night as a kid, although I don’t remember that. But I do remember singing all the time from a really early age.

“My grandad had this CD of Scottish songs and the first songs I learned as a kid were things like A Wee Deoch An’ Doris and Donald, Where’s Your Troosers. I also knew all the words to I Belong To Glasgow, even though my grandad was not from there.”

But he admits his singing made it tough for him at school.

“I was also quite good at sports and played football and got Higher PE, but I still got bullied for being a singer. Kids can be horrible when they find out you go to musical theatre classes.

“But the last laugh is on me. I have done all right as a singer – and one of the guys who used to bully me is now in jail.”

Keith lives with his girlfriend dancer Alana Macfarlane in a flat in London. They met when she was a dancer on his first album tour.

So how does he cope with the attention of lots of young ladies?

“You do get all kinds of groupies in this business, from 18 to 98, and they say they want to take me home,” he says. “But Alana’s great about it. She laughs and says ‘You want to take him home? On you go!’”

Refreshingly, he believes he is still watching and learning from those around him. “I learn every day,” he says. “I am so lucky to be in a show with a great cast and I have a top producer in Bill Kenwright looking over me. How can I not learn from people like that?”

He is glad he did not win the BBC’s Joseph contest. With the benefit of hindsight he now believes it was better to come second.

“Lee was more ready than me for the role. I was too young. In the two or three years that have gone by I have really grown up and am more prepared.”

But Lee did go on to marry Denise Van Outen …

“Yes, and good luck to him,” says Keith, laughing. “But I’ve got Alana – and have you seen pictures of her? She’s gorgeous. ”

It seems Bill Kenwright was simply waiting for him to mature, bringing him on via the Narrator role before casting him as the lead. Keith is now using his star status to put something back, to encourage other kids into the business. He and Alana set up a musical theatre summer school in Edinburgh.

He said: “We had 250 kids turning up over the summer and now we want to bring it to Glasgow. I really love teaching, letting young people know that musical theatre can make the dream come true.”

  • Joseph And The Amazing Technicolor Dreamcoat, King’s Theatre, Glasgow, September 14-19, £24-£33. 0844 8717627