Security guards will be able to search pupils for knives at the school gates without their consent under government guidance to be published today. Schools will also be able to use security arches and metal detector wands when they search pupils for violent weapons.

Legislation passed last year giving teachers power to search pupils for knives and other offensive weapons without consent comes into effect today. But guidance to headteachers from the Department for Education and Skills, published for the first time today, shows how schools can use the new powers. It makes plain that screening and searching can be carried out by professionally trained security staff, as well as teachers. However, it adds that where there is any risk to safety, police should be called.

Security guards would be asked by headteachers to do the work if they felt it necessary. They would have to be vetted with checks by the Criminal Records Bureau, the department said. Guards would also be able to search pupils without their consent. Under the plans, parents would be told annually by schools that a searching policy was in place.

Education department officials insisted last night that the problem of knives in schools was not a large one, but that the powers were needed to deal with the small minority of serious cases. The department emphasised on its website: “We adopted these policies because the Government wants to prevent knife-carrying getting any hold among our young people, including in schools. It would be wrong to exaggerate the scale of knife-carrying in schools: incidents are very rare.”

However, a Youth Justice Board survey found that 33,000 of 11 to 16-year-olds had admitted carrying a knife in school.

In 2004 there were 170 convictions of under16s for carrying a knife, 37 for carrying them within a school.

Alan Johnson, the Education Secretary and a Labour deputy leadership contender, said last night: “Every child has the right to learn in a secure and safe environment. The main way to keep knives out of our schools is to continue educating young people about the dangers associated with illegally carrying a knife. But one violent crime caused by a weapon is one too many.”

He said that the new power was called for by teachers, “but our guidance makes clear that a search should never take place where there is any risk to staff or pupils. In those circumstances the police should be called.”

He added: “Schools can also use metal detector arches and wands to screen pupils for knives where the head feels this is helpful. I think parents will welcome the clear message that bringing a weapon into school is a criminal offence and will not be tolerated.”

Parents and headteachers last night backed the move.

Margaret Morrissey, of the National Confederation of Parent Teacher Associations, said: “I cannot see any other solution, because I really think it’s one ask too many to call on teachers to frisk and remove knives from young people.”

John Dunford, general secretary of the Association of School and College Leaders, said that the powers sent out a strong message that schools would not tolerate violence.

“Most schools will continue to do what they have always done, which is to call in the police when they suspect weapons are involved. Heads and teachers are well aware of the potential dangers and will not put themselves at risk.”

The guidance advises heads how to screen pupils and suggests that randomly selected group of pupils, such as a class, could be screened in order to send a strong deterrent message. It also says that pupils can be refused entry to a school if they refuse to be screened.

The power applies to schools and further education establishments in England.

It was originally contained in the Violent Crime Reduction Act 2006 and is brought into force today.

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