They have been given the backing of the National Association of Head Teachers to intervene physically when pupils are fighting, risking injury to others or disrupting classes.

In the past, teachers have often been reluctant to step in for fear that their actions could result in accusations of assault.

Issuing the advice to his members, the General Secretary of the National Association of Head Teachers, David Hart, said: "For far too long teachers have been kept in a state of limbo over when they can use reasonable force to control or restrain pupils.

"Too often they have understandably been afraid of malicious or unfounded accusations of child abuse.

"Teachers do not expect to be given special protection if they use reasonable force, but they are entitled to be safe from prosecution where they use reasonable force in justified circumstances."

Closely following government guidance issued late last year, the union says reasonable force should be used in self defence, where there is a risk of injury or significant damage to property, or where "good order and discipline are compromised".

'Force must be proportionate'

This could cover fights, acts of vandalism and "rough play" by children, and children running in a corridor and risking injury to themselves or others.

Reasonable force could also be used against a pupil who tried to abscond from a class, refused an order to leave a lesson, or who seriously disrupted lessons for other children.

The guidance stresses that intervention must be proportionate and take into account the "age, understanding and sex of the pupil".

Actions which could be construed as "reasonable force" include:

• Standing between fighting pupils
  
• Standing in the way of a pupil
  
• Holding, pushing or pulling a pupil
  
• Leading a pupil away from an incident by the hand, or by "gentle pressure in the centre of the back".