Two 15-year-old boys at Bramhall High School in Stockport, Greater Manchester, had already been found by Scuba the labrador to be in possession of cannabis, and had been suspended from lessons.

Kevin Bocquet: "The school may use the same tactic without warning again"

The headteacher, John Peckham, said he reserved the right to continue with the spot checks. He believed his school was the first in the UK to copy a practice used widely in the United States.

He denied that using the sniffer dog would send out the message that his school suffered badly from drug abuse.

John Peckham: "Every school in the country has a problem with drugs"

"Every school in the country has a problem with drugs - ours is no better or no worse than any other," said Mr Peckham.

"We see this as being part of a comprehensive strategy to reduce the harm that drugs cause to young people.

"Just as the fear of breath tests deters many adults from drinking and driving, so the very remote possibility of being caught in school with an illegal drug will also act as a deterrent for many young people."

He added that although there had been a couple of letters of complaint from concerned parents, the response had been broadly favourable.

The chair of Bramhall High School's governors, Suzanne Wyatt, said she was confident that her school's reputation would not suffer in the eyes of parents.

But the policy was not supported by Stockport's Chief Education Officer, Max Hunt.

He warned that the sight of a sniffer dog might worry younger pupils at the school, which has 1,450 pupils aged 11 to 16.

Daniel Hyde, 16, welcolmed the school's tough stance on drugs but added: "I don't think it's done much for trust between staff and the students."

Rachel Young, 13, supported the move. "You don't want young kids getting forced into drugs and getting hooked on them," she said.

The dog's handler, Steve Warren of Sovereign Security, said his normal working environment was in night clubs.