One in a hundred people has a stammer. There is no cure but there is hope.

As a child Ashley Guerin would do his best not to speak. His stock answer at school was: 'I ain't sure,' and he is sure some teachers assumed he was either ignorant or insolent.

He was neither. Instead he had a severe stammer.

On Tuesday he is part of a documentary following a group of people through an intensive course to help them gain some control over debilitating stammers.

It was a course Ashley first took, aged 17, and which has been part of his life ever since. It also changed his life, enabling the almost silent teenager to become a businessman running his own building company and comfortable talking to strangers, making phone calls and delivering speeches in front of hundreds of people.

'My speech was really bad. I used to struggle with every single word and just tried to avoid speaking altogether. I'd been through all the usual speech therapy and there wasn't anything that really helped,' he said.

Like most stammerers, Ashley's speech problems began when he was around three and affected just about every aspect of his life. 'I decided to get a job in IT, even though I hated IT, because I thought I wouldn't have to talk!' he said.

Now 37, and running his own building construction company from his home near Norwich, he is due to get married in September.

'I thought my stammer meant I would never find a partner,' he admitted. In fact, his stammer helped him find a partner as he met his fiancé, Clairemarie, through the McGuire Programme – a therapy developed by a stammerer (or stutterer – the two words both mean the same) which trains people in a breathing technique to help them speak.

Ashley and Clairemaire are both now teachers with the programme.

The initial course is an intensive four-day programme and, once the breathing technique is mastered, includes exercises such as beginning conversations with strangers, learning how to stammer on purpose to overcome anxiety about being unable to speak, and delivering a speech.

Most people then return regularly to keep on top of their stammer. 'It isn't a cure, it's a technique to control your speech,' said Ashley. 'If I stopped attending courses I would struggle. It's like sport. You have to keep training.'

He admits being disappointed after his first course that there was not a huge, immediate and permanent change. Now he believes the technique has the potential to work for most people – but involves a huge amount of effort. 'You have to face all your fears. And every time you stammer, you should try to stop and start speaking again.

'Once you have learnt the technique you have to go out on to the street with a coach and talk to 100 people. You might ask directions, ask the time, tell them you are on a speech course, it's not what you say that's important, it's the fact that you are having to talk to people. The first time I only managed about 14 or 15 people, I was petrified. But once you have signed up it's a lifetime membership and you can come back again and again.'

Remembering his own fear, as a teenager, Ashley, now an instructor and coach, is well aware of how 13-year-old Riley is feeling during the ITV documentary to be shown on Tuesday.

'When he started he was very, very quiet. I knew what he was going through and he gained so much confidence!' said Ashley.

And although Ashley still has to work hard to keep his stammer under control, he is fluent and fascinating chatting on the phone.

'I don't try and avoid stuff any more,' he said.

Instead he has travelled to Dubai, the USA, Canada and Mexico to help coach fellow stammerers, as well as dealing with all the interactions of day-to-day life and running Guerin Construction. 'A few times you get the odd impatient person, or someone who laughs, but from childhood I've had really good friends around me. Years ago I would rather pretend to be stupid than try to speak but now I tell people about how I work on my speech.'

For more information on the McGuire Programme visit www.mcguireprogramme.com

Watch Ashley Guerin taking part in School for Stammering on ITV1 at 9pm on Tuesday, January 9.

The one-off documentary follows the emotionally-charged journey of six people as they attempt to control their stammers and change their lives. A lorry driver, a teacher, a pharmacist, a photographer and two schoolboys take part in the intensive residential four-day course, filmed for the programme. Some go from being unable to speak to giving a speech in front of hundreds of strangers in Trafalgar Square. Ashley Guerin, from Norwich, helps coach 13-year-old Riley, who has stammered all his life. Before starting the course Riley tells viewers he feels like a jigsaw with missing pieces and if the pieces aren't found, he's unrepairable, which makes him really sad.