Ministers have hugely exaggerated the number of new teachers recruited since 1997, according to the Conservatives. Last year the Government welcomed new staffing statistics showing that there were 36,200 more teachers working in English schools than when it first came to power.

But the real net gain in full-time qualified teachers over that period was just 3,100 once retirements and teachers leaving the profession were taken into account, the Conservatives said.

Their figures, obtained through a Parliamentary question, also revealed that the number of teachers leaving full-time service to go part-time had risen from 6,910 in 199798 to 11,660 in 200405.

David Willetts, shadow education secretary, believes an incoming Conservative government would face a teacher retention and recruitment challenge. He wants to reach a new settlement with teachers and is proposing a professional structure to “protect them from fads and fashions”.

The Conservatives have been inspired by the US agency set up under George Bush’s No Child Left Behind legislation to collect empirical evidence about what works in the classroom.

This week, David Cameron, Conservative leader, proposed helping heads by allowing them to buy education for the disruptive pupils they permanently exclude, and reducing the number of exclusions overturned by appeals.

Pupil referral units were few and far between and provided inadequate education, Mr Cameron said. “We should open up the provision of remedial education and supervisory work to the private and voluntary sectors, putting budgets in the hands of heads.”

Conservatives also suggested merging the General Teaching Council, Teacher Development Agency and National College for School for Leadership to strengthen the profession. And the party wants to counter a shortage of advice within the Department for Education and Skills and reduce its reliance on consultants by creating a chief education adviser.

Alan Johnson, Education Secretary, said pupil referral unit places had doubled since 1997. And a spokesman for his department said there had been a rise in the number of full-time equivalent teachers from 399,200 in 1997 to 435,600 in 2006, which was a “good news story”. But the Government figures include a 12-fold increase in on-the-job trainees and a huge rise in unqualified instructors and overseas teachers.

John Howson, a Liberal Democrat education adviser, said the Government’s claim was disingenuous, as there had been no improvement in pupil-teacher ratios, because of increased secondary rolls.