EXPERTS have warned that random drug testing in schools could encourage pupils to switch from cannabis to heroin which clears the body more quickly.

Faversham's Abbey School is the first state school in the country to carry out random drug testing of pupils and headmaster Peter Walker says the results so far are positive.

He said pupils are proud that the school is being proactive about drug taking and testing has helped pupils resist peer pressure.

"It is early days in the experiment but some signs of success are already showing themselves," he said.

But Professor Neil McKeganey, of Glasgow University's Centre for Drug Misuse Research, says there is no proof the schemes work and they could have negative spin-offs.

He said tests could damage the relationship between pupils and teachers and may encourage pupils to switch from cannabis to drugs like heroin which clear the body more quickly.

He also said testing programmes could lead to an escalation in attempts to conceal illegal drug taking rather than reducing its use.

Professor Neil McKeganey warned against random drug testing until there is "clear data" on its effectiveness.

The government has given English schools the freedom to test and the Conservatives are pledging increased funding.

The report, published by the Joseph Rowntree Foundation, has called for more study into the impact of testing.