The shortage of primary headteachers is now so dire that schools are searching for temps to fill the vacancies, says the National Association of Head Teachers.
David Hart, the union's general secretary, has urged the Government to abandon its "slavish adherence" to Tory spending plans in order to stave off the gathering recruitment crisis. Salaries, he says, need to be substantially increased.
In a letter to the Education and Employment Secretary Mr Hart warns that the shortage of heads and deputies is now the worst in a decade.
New figures show that 20 per cent of all headships need to be readvertised - a figure rising to 50 per cent in London.
Teacher recruitment agencies like Protem and Capstan are already advertising for "locum" heads to fill vacancies temporarily, and it is impossible to fill even acting heads' posts in some London boroughs.
According to Mr Hart, heads and deputies are paid about10 per cent less than managers in the private sector. By next year they will be further behind. He said more and more teachers believe that salary increases received as a result of promotion to headships and deputy headships were "not worth the candle".
In his letter to Mr Blunkett, Mr Hart writes: "Unless the School Teachers' Review Body is directed specifically to consider the recruitment, retention and motivation issues related to, and the pay levels of, heads and deputies, the crisis can only get worse. This will not assist your Government's drive to raise standards."
According to the NAHT, the new Government can well afford substantial pay rises because the economy is in much better shape than ministers are letting on.
In a separate announcement, Mr Hart this week called for a Pounds 4 billion increase in the education budget.
"The Labour Government is giving the clear impression that the state of public sector finances is dire and that therefore it needs to hold to the previous government's expenditure policy.
"But we have no doubt that in fact the economy is very strong indeed. Heads will find it extremely difficult to understand why the Government intends to clamp down on public pay for at least another year.
"We need a significant change of approach if the Government is to fulfil its manifesto promise to devote a greater share of public money to education. "
"The Government knows only too well that heads are absolutely crucial to the success of its drive to raise standards," said Mr Hart. The mass exodus of experienced headteachers and deputies this year and the mounting evidence of recruitment difficulties across the country does not augur well.
"We look to the Education Secretary to put the interests of schools before slavish adherence to the previous government's pay policy."