Dawn-to-dusk school day 'is a threat to family life'

They said the 50-hour school week - designed to help mothers return to work - will further separate children from their parents.

From 2010, primary schools will offer 'wraparound' childcare between 8am and 6pm. Secondaries will run breakfast and after-school clubs for under-14s.

Addressing the NASUWT conference, headmaster Stuart Merry said children with difficult home lives might benefit from the scheme.

"They are actually better off being with someone who's qualified, getting a decent breakfast and having some care afterwards," said Mr Merry, the head of Emley First School in Huddersfield.

"But some people will just see this as just another way of dropping off children so they can get on with their busy lives. I don't think schools should be in the business of encouraging that.

"There are two sides to this debate - the deprivation in terms of social care and the deprivation of not seeing your parents."

Tony Blair himself launched the plan to help "latch key kids" who return to empty homes after school.

Conference delegate Paul Bullimore said: "How does keeping children at school for ten hours a day fit in with Mr Blair's idea of the family unit?"

Another delegate, Peter Cull, warned that teachers were already being made to act as social workers. He cited a case where police had asked teachers to resolve a conflict between two students and their parents.

Campaigners have already voiced doubts about the extended hours. Mick Brookes, the general secretary of National Association of Head Teachers, has accused ministers of turning schools into a "national baby-sitting service".

However Chris Keates, NASUWT general secretary, said: "Some people have no choice and have to go to work. What is better - to have approved childcare with professionals or being forced not to work because there is no proper provision?"