Sir John said hand-held scanners were 'in the pipeline'

Metropolitan Police Commissioner Sir John Stevens said two �100,000 devices would be offered initially to schools in the London area where there were particular concerns about weapons.

However the scheme could be extended to the rest of the country.

His offer comes after a 16-year-old boy was convicted this week of murdering Luke Walmsley at a Lincolnshire school.

Alan Pennell stabbed the 14-year-old in a corridor at Birkbeck College in North Somercotes, last November.

The scanners, originally used to spot drugs and firearms, use low-level X-rays to penetrate clothes rather than the body and produce digital images on screen.

Head teachers have welcomed the plan.

'Hotspots'

"We would use them in any place the headmaster felt there was a problem with knives," Sir John said.

"We would also work with the headmaster in hotspots outside schools... places where we know knives are carried."

Sir John told the Sunday Telegraph newspaper the Metropolitan Police owned two of the 4ft-long, US-made Secure 1000 scanners and more - including hand-held scanners - were "in the pipeline".

Pennell stabbed Luke Walmsley through the heart at school

The scanners are similar to an airport luggage scanner and were first used in April in a drugs and guns crackdown in east London.

General secretary of the National Association of Head Teachers David Hart said he hoped other police forces would follow suit.

"I very much welcome the Metropolitan Police Commissioner's offer," he said.

"We need to offer schools with particular problems the opportunity to use scanners to detect knives and other offensive weapons."

He said while there was no case for making every school use extreme protection measures, those with a weapons problem should have the chance to use otherwise unaffordable technology.