The airport-style detectors will not be used randomly

Tollbar Business and Enterprise College in New Waltham, near Grimsby, has used the airport-style devices "a couple of times", principal David Hampson said.

"We use them if we have any kind of suspicion. We do not use them at random," he said.

Jayne Walmsley, whose son Luke was stabbed to death at another school in Lincolnshire, has welcomed the move.

I would rather have kids searched randomly so no one can claim to be victimised, but this is a big step in the right direction Jayne Walmsley

The North East Lincolnshire school has stressed it does not have a knife or drug problem and said the handheld scanners had been bought as a precaution.

Mr Hampson explained: "They were bought to search children for any metal object including mobile phones, a blade or any foil that could be used to wrap a drug-related substance."

The college's vice-principal, David Riden, said the device would only be used "on a very selective basis" and only after suspicions had been raised that a student was carrying something that was banned from school.

"It would confirm our suspicions one way or the other," Mr Riden added.

If a student refused to be scanned by the detector, his or her parents would be asked to remove the student from the school.

Knives campaign

Luke Walmsley was murdered at Birkbeck School in North Somercotes 14 miles away from Tollbar, in November 2003.

Since Luke's death, Mrs Walmsley, from Cleethorpes, has campaigned for a minimum five-year sentence for people found to be carrying knives.

"I hope more schools follow this lead," she said.

"I would rather have kids searched randomly so no one can claim to be victimised but this is a big step in the right direction."

Although the detectors will be used to scan for knives, Mr Hampson revealed they had been largely catching children with mobile phones, which are banned on school grounds.