Image copyright Ryan Longmuir Image caption Ryan's life had spiralled out of control in his teens

At his lowest point, Ryan Longmuir took drugs every day "just to feel normal".

He was also dealing them, and at one point faced a possible jail sentence.

Born in the Scottish new town of Cumbernauld, Ryan began experimenting with drugs when he was 12, initially because he was curious and had fallen in with likeminded friends.

"I tried everything - cocaine, Valium, ecstasy, speed, heroin... I'd go on benders for two or three days at a time, and I'd take five or 10 ecstasy tablets in one night," he says.

"From the age of 15 to 20 I took drugs every single day."

Thankfully for Ryan, everything changed when he was 20, and he has not touched drugs ever since. While the cynical may raise their eyebrows, Ryan, now 37, says he discovered God and quit overnight.

Without the drugs, he was able to get his life back, and aged 24 he launched a catering company called Regis Banqueting.

Today the 13-year-old business has blue-chip clients including mobile phone network O2, luxury carmaker Bentley, and investment bank JP Morgan.

Image copyright Ryan Longmuir Image caption Ryan says that becoming a Christian changed his life

With drugs his main interest and income at the time, Ryan left school in Cumbernauld, 13 miles north-east of Glasgow, aged 16.

Four years later he was dealing thousands of pounds worth of drugs a week, and if he continued he says it was clear that he would become a "big time gangster drug dealer".

Trying to run away from his lifestyle, Ryan decided in 2000 to go to New Zealand for a year in search of a fresh start.

But it fell apart just two weeks after he arrived, when New Zealand customs intercepted a package of 100 ecstasy pills that Ryan had posted to himself from Scotland.

Facing a jail term, he phoned a friend back in Scotland. She said that she would pray for him and suggested he do the same.

Ryan says: "I thought 'you're off your head' but I decided to try it, and I got down beside my bed and I said, 'I don't believe that there is a God, but if you're real then show me that you're real and I'll believe in you.'"

Out on bail, Ryan had to go to the police station every two days, but his appetite for drugs was undiminished.

It was only when he met two female hitchhikers that things changed. The women took him out for lunch, then to church, and allowed him to move in to their home.

"That was when I thought there was maybe something to this because why would two complete strangers do that? That was the catalyst for change."

Ryan says that discovering his faith was fast, and the change immediate. Drugs suddenly lost all appeal, and he threw all the substances that he had into the sea, and has been clean ever since.

"I know most people who have been taking drugs don't have that experience. Most people do ok for a bit then they relapse. Everyone's journey is different but that was mine."

While Ryan escaped jail time in New Zealand, his visa was revoked, and he returned to Scotland in May 2000.

He joined a church, the evangelical Freedom City Church in Cumbernauld, met his wife and got married.

Image copyright Malcolm Cochrane Image caption Tea is now Ryan's drink of choice

To earn money he got a job working with drug and alcohol addicts, where he was able to draw on his own experience to try to help others to quit.

However, when the funding for his role ran out a few years later he found himself without work. It was then that the opportunity to start his own business came about.

His church wanted a catering company to run the cafe attached to their conference centre on an ad hoc basis, and the then-pastor suggested Ryan might fit the bill.

Despite having little to no catering experience he jumped at the chance and Regis Banqueting was formed. Ryan attended catering college alongside running the cafe and learned as he went along.

"I had to phone my mother-in-law to ask how you make steak pie," he says.

Image copyright Regis Banqueting Image caption The company has a number of blue-chip clients

"I was young and naive. If I knew what I know now, I probably wouldn't have started it."

To help Ryan expand the business into contract catering, the Princes Trust, the UK start-up support charity led by the Prince of Wales, gave him a £5,000 loan.

While Ryan says the first three years were tough, with him taking a salary of just £6,000 in year one, over time the clients and contracts got bigger.

Cumbernauld-based Regis Banqueting now has 65 staff - 20 full-time and 40 part-time, many of whom are seasonal - and annual turnover is £1.3m.

Meanwhile, Ryan and the company have won a number of awards including the Royal Bank of Scotland's young business of the year crown, and director of the year from the Institute of Directors organisation.

Image copyright Regis Banqueting Image caption Ryan is now starting another company, alongside Regis

Prof Eleanor Shaw, head of the Hunter Centre for Entrepreneurship at the University of Strathclyde, says it is Ryan's motivation and enthusiasm that helps make him such a success.

"Catering is a really difficult market to be competitive in, but he has such energy," she says. "He's very hardworking and is so motivated that it brushes off on everyone around him."

Looking back on his troubled youth, Ryan says he knows that his life might have turned out very differently.

As a result he tries to help others who face addiction and poverty, for instance by employing former addicts and ex-offenders among his staff.

He is also in the process of starting another company, alongside Regis, that will focus on creating a brand of casual dining restaurants, the first to be launched in Glasgow next year. The plan is to expand across Scotland and the UK before going international.

"I say to my wife sometimes that it's amazing how we're making more money than a doctor or lawyer - and we're making sandwiches," says Ryan.

Follow The Boss series editor Will Smale on Twitter @WillSmale1