Teachers have criticised government proposals to set up random drug-testing in schools.

The prime minister told the News of the World that head teachers would be given new powers next month to demand urine tests of pupils or bring sniffer dogs into class.

John Dunford, general secretary of the Secondary Heads Association, said: "Yet another burden is being placed on schools, which have a contribution to make to solving the drugs problem but policies must look much more widely."

Jean Gemmell, general secretary of the Professional Association of Teachers, added: “My first reaction was to be fairly horrified, mostly because I cannot quite see how on earth it is going to work.

“As a former head and someone who represents teachers, it is adding to their burden of social responsibility to the point that it becomes untenable.”