The threat by the two largest teaching unions was made after the draft Price-waterhouseCoopers report, commissioned by the Government, failed to propose a limit on teachers’ contact time. The unions had suspended action in April when ministers promised to hold the workload review.

Unions were also angered by a speech by Education Secretary Estelle Morris, heralding a change in the law to allow classroom assistants to take charge of lessons in teachers’ absence.

Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers, said it would not look good, if, after eight years in office, the Government’s biggest achievement was to replace qualified teachers with “pig-ignorant peasants”.

Ms Morris’s plan, which she admitted was a risk, followed an admission that the Government would not be able to recruit enough teachers to meet demand over the next four years. She said that schools needed to learn from the experience of hospitals and use “para-professionals” such as classroom assistants, secretarial staff and technicians to fill the gap - a call echoed by the report.

Ms Morris admitted that assistants would need better pay and more training. However, she will be unable to promise extra money until the outcome of the next three-year review of government spending. Chancellor Gordon Brown is not due to announce the results until June, which may also hamper efforts to reach a settlement with the unions.

“I’m extremely disappointed. We have taken a step backwards,” said Mr de Gruchy.

He said that his members would not wait for the School Teachers’ Review Body report in February before moving to industrial action.

John Bangs, head of education at the National Union of Teachers, accused PricewaterhouseCoopers of “pulling its punches” under government pressure. Referring to Ms Morris’s speech he said: “We can’t have any more visions for the future. What we need now are concrete actions. The next two months will be crucial.”

The Association of Teachers and Lecturers, the third largest union, would also consider joining in any action if progress is not made.

A DFES spokesperson said: “We recognise that there are workload issues, that is why there is an independent review. Any industrial action would be highly irresponsible.”

Carol Adams, chief executive of the General Teaching Council, also questioned the Government’s strategy.

“I am totally in favour of classroom assistants but they do not free up time for teachers. Support for learning in the classroom actually requires more time for planning together,” she said. “They should not be used to replace teachers.”

Headteachers’ leaders also attacked the PWC report saying that it put too much emphasis on managing workload and not enough on reducing it and would do nothing for heads.

How effective additional Government money for classroom assistants would be has been brought into question by new research showing that one in five headteachers had to get rid of assistants just a year after Tony Blair announced pound;400 million for more support in schools. The Open University study shows that heads had to make cuts because of school budget pressures.

The researchers claim that the money poured into the scheme to provide 20,000 extra assistants by 2006 has been spent on safeguarding jobs rather than creating new ones. There are 95,000 classroom assistants in schools in England. Only half are on permanent contracts.

The Economic and Social Research Council-funded study was based on evidence gathered from 500 primaries. Its findings come as teaching assistants in the West Midlands face pay cuts of up to pound;800 under plans to implement a new national agreement for local government workers.

Briefing, 26

Classroom assistants: the workload solution? Have your say at www.tes.co.uk