Unison has responded to a dramatic increase in attacks by pupils on support staff, such as classroom assistants, in the first six months of this year - rising from 45 in the same period last year to 107.

The union says that the government's emphasis on keeping disruptive children within school, rather than excluding them, has meant exposing staff to the threat of violent pupils.

Nigel de Gruchy of the NASUWT has warned that cutting exclusions could threaten safety

"Staff are entitled to a safe working environment - and it seems a short-sighted policy to set limits on the numbers of pupils who can be expelled."

"If pupils know that it is almost impossible for them to be excluded, it is going to be very disempowering for the teachers," said Tina Ashley, the union's senior regional officer.

In line with government policy, the city's schools have been reducing the number of exclusions. The education secretary has been pushing for a third fewer exclusions, as part of its campaign against children missing out on education through exclusion or truancy.

Southampton City Council says that a better reporting system is a contributory factor in the sudden increase. It also says that 'attacks' are broadly defined and almost all are of a minor nature.

The council says that it supports the government's policy on "social inclusion", which has sought to reverse the trend for schools to expel problem pupils and to tackle behavioural difficulties within schools.

Earlier this month there were warnings from teachers' unions that stopping exclusions could lead to teachers becoming the victims of attacks.

The National Union of Schoolmasters Union of Women Teachers has warned that schools are being forced to take back pupils who should be excluded - at the risk of the safety of teachers and the disruption of other pupils' education.