A reformed gambler has been called in to lecture students at Wimbledon private school King's College after fears students were staying up late hooked on internet poker.

Head of pastoral care at the 12,000-a-year private school, Kevin Hawney, said a group of boys were staying up late playing online gambling games and missing their studies.

The school in Southside, Wimbledon, has about 1,200 students - 450 juniors and 750 in the senior school.

"It became clear that two boys had become absorbed by online gambling," Mr Hawney told the Sunday Telegraph.

"While I would question the extent to which you could call it an addiction, a lot of time was taken up playing, sometimes late into the night.

"They were then not studying properly and not in a fit state to study."

The school brought in parents to discuss the problem and heads of house were made aware of the issue generally.

"Anecdotally, it seemed around five boys might be at risk," said Mr Hawney.

"It was never clear how much they were betting.

"The pupils said it was not a lot of money - obviously they were defensive about it.

"That's why it is useful to talk to parents, as the money has to come from somewhere"

After the incident, the school, which already covered gambling in personal, health and social education lessons, brought in Reg Starkey, a reformed compulsive gambler, on January 8 to speak to sixth-formers about the dangers of becoming hooked on betting.

Mr Starkey said he told the students his "rags to riches to rags story" in a 40-minute presentation followed by questions.

"What I lost was two marriages, at least one business, and nearly lost my children," Mr Starkey said.

Mr Starkey, 66, a freelance copywriter in between his speaking engagements, said it was "frightening" how easy gambling had become.

"It's so accessable," Mr Starkey said.

"Gambling is on of those very dangerous addictions because there are no substances involved.

"I just want to say to kids there are invisible lines in heavy, addictive gambling they can cross.

"Because it's invisible, it's very easy to cross."

Mr Hawney said it was fortunate the school had the resources and the level of pastoral care to address these kinds of problems.

A spokesman for Gamblers Anonymous said the organisation regularly visited schools to speak to pupils but declined to provide further details.

Gamblers Anonymous have a 10-point checklist on their website, www.gamblersanonymous.org.uk, for young people.

Symptoms of problem gambling include staying away from school or work to bet, using it to escape "a boring and unhappy life" or stolen, lied or borrowed money to feed their addiction.

Gambling researchers fear there are growing numbers of children becoming hooked as new technology made gaming easier to find.

According to the International Gaming Research Unit at Nottingham Trent University, about 3.5 per cent of 11 to 15-year-olds have a gambling problem.

In a recent study of more than 8,000 youngsters, a quarter admitted to gambling in the previous week.

It said the more money the child had, the more often they gambled, with 40 per cent of those earning £30 a week or more had gambled in the past week compared with 21 per cent of those earning £10 a week or less.

It also says boys are far more likely to participate than girls.

Director of the gaming research unit, Professor Mark Griffiths said that adolescent gambling should be taken as seriously as a health and social issue.

"With new technology, children have even more access to ways of gambling," he said. "It is clear that adolescent gambling on the internet and other remote media is likely to become an issue of increasing concern over the next few years."

Prof Griffiths has condemned the Government for being "extremely short-sighted" and contravening its own pledge to protect the most vulnerable from the effects of its gambling liberalisation.

He said slot machines were by far the greatest source of child gambling, but others had admitted to using their parents' accounts to gamble online.

Over the next 18 months, the Responsibility in Gambling Trust, a charity funded by the gambling industry, will run 10 regional seminars and 40 "twilight" sessions to train teachers and youth workers in how to deal with teenage gambling problems.