Children are now experimenting with hard drugs such as heroin and cocaine, according to a leading researcher into drug abuse.
Mr Richard Hartnoll, a senior research psychologist at University College Hospital (UCH), London, said there has been a dramatic rise in the casual use of heroin over the past three years.
As the real cost of buying the drug dropped by half, the number of users in London has doubled, he said. At a street price of around #163;5 a fix, heroin is no more expensive than cannabis.
The result of this is a growing number of young people - some only 15 or 16 - experimenting with the drug.
Mr Hartnoll, who is based at UCH's City Road Crisis Invention Unit, has 10 years' experience of monitoring drug abuse in London.
His findings, soon to be published by the Royal College of Psychiatrists, are based on detailed interviews with "poly drug users" - those who experiment with a variety of drugs.
The replies shed light on the recent report of the Government's Advisory Council on the Misuse of Drugs, which clearly shows that Britain's drug problem is getting worse.
It estimated that there were 40,000 drug abusers, half of whom were regularly using narcotics. This is three times more than the official Home Office figure of 6,157 registered addicts in 1981.
Part of Mr Hartnoll's work has been to probe the extent of drug misuse among children of school age - a notoriously difficult age to research and one of which there is little firm evidence.
He told The TES: "I have been in this field for 10 years, but it has only been in the last couple of years that heroin use in the younger age group has cropped up.
"In particular, schools in the Camden, Westminster, Kensington and Chelsea areas of London, where these chaotic poly drug users have been pupils, or where they have friends, they were experimenting with drugs such as heroin."