The right to frisk pupils suspected of carrying knives, currently being considered by Parliament as part of the Violent Crime Reduction Bill, is worrying heads and teachers’ leaders - but it is already a fact of life in some schools.

In particular, there are worries that heads and teachers will be expected to conduct such searches personally, and that they may be open to litigation for violating students’ rights if they do.

Yet some schools are already carrying out searches.

David Hampson, principal of Tollbar business and enterprise college at New Waltham, near Grimsby, introduced searches last year after setting off airport metal detectors when going on holiday.

As the security guard swept a hand-held scanner around him, he thought:

“That is absolutely spot on. We could use those in school.”

Two such Garrett wand detectors have now become standard pieces of school equipment, enabling hands-off searches to be carried out for knives, wraps of drugs and - the only forbidden objects actually found to date - mobile phones.

“We don’t have a drug or a knife problem in this establishment,” says Mr Hampson, whose college has more than 2,000 pupils aged between 11 and 18.

“It was a question of being pro-active. I liken it to a fire alarm. You don’t wait for the first fire before you install an alarm.

“These detectors make searching someone very easy. There is no physical contact at all and that defuses the situation and saves all the aggravation.

“In the past, here and elsewhere, I have had to do physical searches. You can’t imagine where some youngsters put things - in their bottom cheeks, for instance.

“Patting children down is hard to do properly and there is a risk of accusations.

“It has reached the stage now when I or one of my vice-principals will walk into the classroom with a detector and anyone with a mobile phone will reach into their pockets and hand it over.

“They are not allowed in school, partly because have you ever known a child to keep one switched off? And partly because of the potential for photography.

“We had one young man taking pictures of a rather attractive member of staff he fancied. The detectors bleep loudest for mobile phones, but they will pick up even the smallest coin or wrap of drugs.

“We are very pleased with them and we know the children like them. They make them feel safe.

“The firm we got them from tells us they have had quite a bit of interest since we have been trailblazing.”

Nigel Ingram, director of Regton Metal Detection Specialists in Birmingham, which supplies the pound;150 scanners, predicts that their use will become widespread.

“In the States most schools have hand-held and walk-through detectors, and I think we will go the same way,” he says. “It is just a question of time.

“Tollbar is the catalyst because, although we have supplied some to schools in Glasgow before, Tollbar is the first to talk about it.

“In America, the worst problem is at schools for children aged nine to 14.

Unfortunately, I suspect detectors will spread into some primary schools here too. It is good for business but I’d rather we didn’t have that problem.”

Tim Andrew, president of the Secondary Heads Association, believes most heads will experience at least one incident in their careers when the power to search a pupil would be useful.

“In a school where I worked 20 years ago, there was a scuffle in the corridor and after the kids had disappeared I found a sharp chisel with a long blade lying on the floor,” he says.

“Had I suspected such a thing was being carried I would have been very grateful for the power to search pretty thoroughly for it.

“Luckily, 99 per cent of the time in 99 per cent of schools this is not an issue, but you would be foolish to ignore the statistics that show a significant number of young people these days carry knives.

“I really don’t see schools having airport security-type machines that all school bags go through as the children walk through the gates.

“But for some schools, the reality is that some kids feel safer if they carry something into school, and it is a good thing if heads have the ability to deal with it.

“Currently, if you ask a child to turn out his pockets, and he says no and his parents won’t play ball, you are stymied, which puts you in a very difficult position.”