As an energetic 13-year-old, Callum liked to keep himself occupied, playing football, cycling - and deliberately lighting fires. Just 4ft tall and pencil thin, he is already quite the veteran.

"I've lit between 300 and 400 in all," he says. "If you're talking about the bigger stuff, it's probably around 40. I destroyed a whole playground once by setting light to the petrol from an abandoned motorbike. It burnt the swings, the slides, the tar on the ground, everything. Firefighters would come and we would just chat with them. It was a thrill."

But that was then. Now 14, and apparently no longer a menace to society, he has become a important part of the government's antisocial behaviour strategy.

Last month, in an east London fire station, Callum stood before a group of teenagers and gave them the benefit of his vast experience. "I am Callum," he began gravely. "I am 14 and I used to set fires, but I don't anymore. It's no good."

The government believes children who have an insight into arson, its consequences and the job of fighting fires will curb their offending. It seems to be working. New figures show that the number of arson incidents across the country fell to 75,800 - a 21% reduction over the previous year. The number of cars being set alight fell by 24% over the same period last year compared with 2003.

Jim Fitzpatrick, the minister responsible for fire safety, has directly linked the extraordinary reduction with intervention work being carried out by firefighters working with troubled teenagers.

Callum and more than 1,500 other teenagers have all been through a Local Intervention Fire Education programme (Life), which is run by fire brigades and funded by national and local government, as well as the European Social Fund.

The Life strategy involves nine London boroughs, plus five other brigades in Northern Ireland, North Yorkshire, East Sussex, Hampshire and Hertfordshire. Arson reduction schemes are also being run in Bristol, Staffordshire, Kent, Luton and Northumberland.

More than 50% of all fires in the UK are arsons. They cause 100 deaths a year and 2,500 injuries. It costs the economy £2.8bn, but the cost to society is estimated at £55m a week.

Some 80% who have been through the Life programme had not reoffended after six months. According to Cara Kelly, the Life team leader in Newham, east London, teenagers learning firefighting skills also learn about themselves.

"A lot have previously been told that if they can't pass exams they will never have a job," Kelly says. "They leave here with enough confidence to say they can do this and perhaps there are other things they can do. A lot of firefighters have experienced that same feeling [about the kids]. They are not judgmental."

Insurers are already so pleased at the falling incidence of arson that they are helping to fund diversion projects involving firefighters and converts like Callum.

Preparing to address teenagers at Plaistow fire station, Callum says his firesetting started at four. "I set fire to my mum's bed and her carpet. She realised and came into the room to see me sitting in smoke. I would have matches and lighters on the floor and would play with them to see how high the flames would go. From there I was setting fires to bins and park benches to see them go up. I would spray deodorant on them to see how it affected the fire. I would sit and watch them. You would get a rush. Each time I would think that I had gone too far, but you would soon calm down and do it again."

He says there were few limits to what he would do, though he would avoid buildings with people in them.

There were two turning points for Callum. The first was when a fire got out of hand and his friend's leg caught fire. The second was his expulsion from school and his referral to a unit where other teenagers had completed the Life course, spending a week in a fire station as a trainee crew member. "You look at them doing things and you don't believe you could ever do them, but then you find you can," he says. "I have much more self-confidence. It changes the way you think."

(with thanks to Hugh Muir and The Guardian)