A growing number of teenagers are using cannabis, a survey showed yesterday.

A growing number of teenagers are using cannabis, a survey showed yesterday.

The proportion of 14- and 15-year-old boys who said they had tried the drug jumped from 19 per cent in 1999 to 29 per cent in 2001, according to the Schools Health Education Unit, an independent research group. Cannabis, which is being downgraded from a Class B to a Class C drug, was the only illegal drug not considered to be "always unsafe" by older children, the unit found. Reclassifying the drug will mean that being caught in possession by police will not automatically lead to arrest.

Last week, three studies found frequent cannabis use among young people increased the risk of depression and schizophrenia in later life. One found that people who used cannabis by 15 were four times as likely to experience schizophrenia by 26. And scientists say that one cannabis cigarette contains the same amount of cancer-causing chemicals as five containing tobacco.

More teenage girls are also smoking cannabis, the unit's annual survey showed. In 1999, 18 per cent of 14- and 15-year-old girls said they had smoked it, but in 2001, the proportion was 25 per cent. The unit questioned 15,881 pupils at 334 primary and secondary schools around the UK on a range of social, health and education issues. It found that more teenage boys were using the internet without parental supervision – raising fears they could be looking at hardcore pornography and other unsuitable material.

The proportion of 14- to 15-year-old boys who said they surfed the Net with no supervision rose from 55 per cent in 2000 to 67 per cent last year.

The unit found that 66 per cent of all children now have access to the internet, rising to 81 per cent of 14- and 15-year-olds.

The unit's director, David Regis, said: "The potential exposure of youngsters to [inappropriate material on the internet] has always been a concern. Clearly, the direction of supervision seems to be not what we would like."

Dr Regis also sounded a "health warning" about the drugs figures, saying the schools chosen for the survey changed from year to year and the rises could be attributable partly to that. "Whether this is a general trend or just something about the schools we are using isn't clear from this data."