Announcing the new search powers for teachers, education and skills secretary Alan Johnson said: "Every child has the right to learn in a secure and safe environment. Fortunately knife incidents in schools are extremely rare and the majority of schools will not need to use these measures.

"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.

"This 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. "Schools can also use metal detector arches and wands to screen pupils for knives where the head feels this is helpful and would work as a deterrent.

"I think parents will welcome the clear message that bringing a weapon into school is a criminal offence and will not be tolerated.

"Screening, alongside today's new power for searches, means that schools now have the law behind them so they can take the necessary action to prevent weapons from coming through the front gate."