The first hard evidence of the recruitment problems facing schools emerged this week as the grant-maintained sector revealed that half of secondaries and more than a quarter of primaries were having to re-advertise jobs.

Opted-out schools were often dissatisfied with the quality and number of staff applying for classroom posts and reported a growing shortage of good heads and deputies.

Teacher supply specialists have long warned ministers of the lack of undergraduates willing to train as secondary maths and science teachers and it appears there are now problems recruiting English staff.

The shortages come amid rising class sizes, with pupil:teacher ratios worse this year than they were a decade ago and classes of at least 35 children in a quarter of all primaries in England and Wales.

This week unions told the teachers’ pay review body it must recommend substantial salary rises to stave off the crisis and make teaching - perceived as a badly paid and constantly criticised profession - more attractive.

And the Government was warned that it would have to face the electoral consequences if the review body heeded calls from Kenneth Clarke, the Chancellor, for a lower rise than last year’s as he attempts to curb public spending to finance tax cuts.

Such a settlement appeared to gain support from Gillian Shephard, the Education and Employment Secretary, who described this year’s 3.75 per cent rise as “relatively generous”.

The decision, to be announced early next year, is likely to coincide with the run-up to the general election and could be particularly significant if it adds to parental concern about rising class sizes.

“Increases of 2 or 3 per cent will be another nail in the coffin of this Government,” said Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers.

The four classroom teacher trade unions have united in a single submission to the review body and accused the Government of failing in its responsibility to recruit and retain young entrants.

Shortages of classroom teachers as the recession ends have been widely predicted but the problem has never been accurately quantified. The evidence provided from the Grant-Maintained Schools Advisory Committee to the review body is based on a survey of 400 schools.

There is nothing to suggest that recruitment problems are worse in the GM sector and given its size - just 1,100 schools out of 24,000 nationally - and favoured status, the position could be more serious in the maintained sector.

GM secondary schools experienced difficulties in the core subjects of English, maths, science, design and technology and foreign languages - a wider range than previously suggested. Curriculum co-ordinator posts were the trickiest to fill in opted-out primaries.

Problems were not confined to inner-city schools but included some in both affluent and socially deprived areas.

Previous statistics have covered recruitment of heads and deputies. First indications of research currently being done for the National Association of Head Teachers by John Howson of the Teacher Training Agency are that problems are worse than feared. The situation in special schools is becoming “critical”, he said.

However, the Department for Education and Employment’s submission to the review body asserts that there are generally sufficient teachers to meet schools’ demand, but admitted: “There may be some local difficulties.”

It claimed there were just 558 vacancies for secondary classroom teachers this January - with the worst-hit subjects being languages, then English followed by maths.

The NAHT and the Secondary Heads Association, in an unprecedented move, submitted a joint claim for a “substantial” rise to be funded, while the National Governors Council urged the review body to resist ministerial pressure to introduce performance-related pay.