The threat to jobs comes as schools continue to complain of shortages and despite ministerial promises of a big expansion in the numbers of classroom assistants to be drafted into schools in their workload deal with teacher unions.

Schools had been expecting to reap the benefits of Chancellor Gordon Brown’s “biggest sustained increase in education spending for a generation”.

But headteachers in at least seven local authorities are warning that they will not have enough money to retain existing staff, let alone meet the costs of last month’s workload deal.

Many more authorities will avoid laying off staff through big increases in council tax or by cuts to other services.

The largest support staff union, Unison, has already received calls from members threatened with redundancy.

The worst-hit areas are in southern England. Headteachers in Plymouth say that the jobs of 100 teachers and 200 classroom assistants will go.

Schools in Leicestershire, Essex, Bracknell Forest and the London borough of Bromley will also be affected, a TES survey of 43 of the worst-hit local education authorities reveals.

In York, schools will have to cut jobs after losing around pound;1 million between them from the council’s education budget. Dorset and Liverpool councils said they could not rule out redundancies. Heads in Barnet are also expecting job losses.

Alan Davison, head of Mill Hill county high in Barnet, north London, will lose about five teachers because it has a pound;200,000 budget shortfall.

He said: “There is no question that we will have to lose staff and it is at a time when we should be cutting workload because there are more pupils.”

West Sussex believes its schools can avoid redundancies but has written to parents and schools to warn them that, despite an 18.5 per cent council tax rise, schools face cuts of around pound;40 per pupil.

The National Union of Teachers - the only teaching union to refuse to sign the workload deal - warned that the Government’s standards drive was now under threat.

John Bangs, NUT head of education, said: “The potential is there for schools to delete teaching posts because unqualified staff are cheaper.”

Changes to the council funding system and the scrapping of some direct grants have meant big increases for some areas while others struggle to meet rising costs, such as funding the 2.9 per cent teachers’ pay rise.

Falling pupil numbers have also affected some areas, notably Bracknell Forest and Leicestershire.

Earlier this month, Education Secretary Charles Clarke used new powers to force Croydon and Westminster to increase their schools’ budgets but fewer than half of the councils expecting redundancies passed on less cash to schools than the Government intended them to.

Plymouth has to make pound;14.2m cutbacks in public services despite a 14.75 per cent rise in council tax while schools in Bromley will lose more than pound;2m in standards fund grants.

David Hart, general secretary of the National Association of Headteachers, said that the problem appeared to be “fairly widespread”.

“The Government’s statement that all schools are going to benefit from the extra funding in the system this year is simply not true in some cases.”

The NAHT has threatened to withdraw from the workload agreement if it turns out not to be funded properly. It will take a decision on the issue in the summer after it has a completed a national survey of school budgets.

A spokesman for the Department for Education and Skills said: “We are guaranteeing LEAs a minimum increase of 3.2 per cent per pupil and pressing authorities to pass on increases in school funding. The vast majority have done so.”

Teacher quits, 3 Working harder, 14