Peter Walker, head of the 960-pupil Abbey school in Faversham, has written to parents asking for their consent before a nurse starts taking mouth swabs from pupils.

Teachers have also offered to take part in the experiment, which starts in January. Mr Walker said tests on staff would be voluntary but was unable to say how many had volunteered.

Swabs will be taken from 20 randomly selected youngsters each week.

Results, which take three days to process, will show if pupils have taken cannabis, ecstasy, cocaine or other drugs. Pupils taking drugs will not be expelled but parents will be called in to discuss the problem.

Mr Walker hopes the scheme will raise standards. He said: “Even if parents agree to children taking the tests, no one will be compelled to take part.

But if a pupil refuses, we will ask the parent to come in and discuss why this was the case.

“We do not have a bigger drugs problem than any other school but we are being more pro-active. I want to improve prevention and quality of life for those who don’t take drugs and believe random tests will affect a wider audience than, say, targeted testing.”

Mr Walker, head at the school for 18 years, said evidence showed half of 15-year-olds nationally had experimented with drugs but a huge proportion of those chose not to take drugs further.

He said: “We have to be more pro-active in ensuring fewer children use drugs but I am not living in cloud cuckoo land and am prepared for this experiment to fail.” Dozens of consent forms have already been returned and the scheme, funded by sponsorship will be reviewed after six months.

Allan Craig, National Association of Schoolmasters Union of Women Teachers national executive member for Kent and Medway, has advised staff to boycott the scheme.

He said: “I know that Peter Walker has been at the forefront of dealing with drug abuse, (but) he has not to my knowledge consulted unions and I would advise members not to take part.”