Desperate times call for desperate measures. The Government faces the damaging prospect of children being sent home in their thousands because of the recruitment crisis and resulting industrial action. Ministers simply cannot afford to wait for more newly-qualified teachers to emerge from training colleges.

Already supply agencies are scouring Australia and New Zealand. But Education Secretary David Blunkett is hoping to tap a hidden pool of qualified teachers closer to home.

Letters will soon land on the doormats of 25,000 teachers who retired early in an attempt to persuade them to return to the classroom.

The first 8,000 went out on February 2 but posting is being staged so that the response phone lines don’t get jammed. The letter is part of a “Your Country Needs You”-style campaign to persuade retirees to come back.

Under a bold heading - “New pension arrangements” - the letter from Mr Blunkett begins: “I am writing to you... about some recent changes to pension rules. These make it easier for teachers who took early retirement to do some teaching work with no reduction in their pensions.”

Simultaneously local authorities are running advertising campaigns and the Teacher Training Agency has set up a telephone registration system. Returners are invited to put their names on a national register. Local education authorities will be able to tap in to this to see if there are skills on the register that match their vacancies. Money has been allocated for retraining.

The Blunkett letter offers an apparently juicy carrot: it suggests regulations that meant retired teachers had their pensions temporarily reduced if they earned more than their old salary have been relaxed. But it is not quite as simple as that.

In reality those who come back will be penalised if their new salary plus their pension adds up to more than their “salary of reference” - the highest salary they received in the three years prior to retirement, adjusted for inflation.

Even the Teachers Pensions Agency acknowledges that the letter is “a little bit misleading”, as the mostly technical changes to which it refers were introduced 18 months ago.

As part of the campaign, the agency has set up a website with a calculator that allows retired teachers to work out how much they can earn without affecting their pension (see box, right).

And as well as tweaking pension regulations, the Department for Education and Employment has now, for the first time, publicly admitted that retired teachers can work for supply agencies without affecting their pensions - something of which most unions were not aware.

The pool of teachers who have retired early is potentially significant. There was a sharp rise in early retirements in 1996 and 1997 sparked by the decision of John Major’s Conservative government to change the rules.

While in the past most teachers who retired early did so with an enhanced pension, this is now usually restricted to staff at schools that are being reorganised or closed. Teachers over 55 can still retire voluntarily, but must accept a reduced pension.

Early retirements rose steadily through the 1990s, from 9,080 a year in 1995-6 to 10,730 in 1996-7 and 12,600 in 1997-8, before falling sharply to a mere 2,520 when the new rules came in.

Those who retire without an enhanced pension have always been eligible to continue to work without any cut in their pension.

What is at issue now, however, is how many of the early retirees might want to return.

A DFEE spokesperson said that it was too early to say how many were interested but described the initial response as “encouraging”.

The Local Government Association Employers’ Organ-isation thinks the appeal can work and supply agencies report a rise in interest from retired teachers.

The headteachers’ unions are also optimistic. The National Association of Headteachers and the Secondary Heads’ Association both report a significantly increased number of calls from members.

However, many are interested in using another route to fill vacancies - so-called “down-stepping”. This allows senior managers to return to classroom teaching while protecting their higher-rate pension. Previously this was only allowed within the authority for which they work but it has recently been extended to allow them to move around the country.

And despite reports of interest in the scheme from their unions, many heads doubt whether staff can be enticed back.

Tim Andrew, head of Chesham high school in Buckinghamshire, says: “We’ve got one retired teacher who is going to come back to cover maternity leave. But she’s doing us a favour.

“If I’d retired and got my life organised, I’m not sure I’d return to help the Government’s recruitment problem. It’s not as if our good friend David can wave his magic wand and all the teachers will come flooding back.”

Alan Smithies, head of Speke community school in Liverpool says: “Get retired teachers to come back? No chance! The fact that they were granted early retirement means that there was probably some kind of fatigue or exhaustion. I’m laughing because I’m wondering what’s behind the move. Is it a shot in the dark? It might work for nurses. I don’t think it’s going to help us.”

Professor John Howson, a specialist in teacher recruitment, is also sceptical.

He says: “In the past it has not been a significant route into the profession. There have not been significant numbers leaving early in the past couple of years. The longer they are out of the classroom the less likely they are to want to come back. It may help at the margin but it’s not going to solve the problem.”

Indeed, a joint TESSHA survey of teacher vacancies, published last week, suggests that there may be as many as 10,000 posts unfilled in English and Welsh secondaries.

And although the number of retired staff returning has increased slightly over the past decade only around 1,400 teachers (including primary) come back to the profession every year - and 1,200 of these do so part-time.

If more teachers are tempted back it could make a big short-term difference to teachers and pupils at individual schools. Any initiative that could provide a specialist maths teacher for a class that has been making do with a succession of supply teachers or a non-specialist will be welcomed.

But wooing back retired teachers looks unlikely to have a significant impact on the recruitment crisis. Many will be reluctant to return to the classroom and even those who do will be fast-approaching retirement age, And, according to Professor Howson the campaign could make matters worse. “In areas where there is no shortage or if those returning teach non-shortage subjects they could take jobs from newly qualified teachers,” he says.

If that happens then ministers’ attempts at a quick-fix may only prolong the recruitment problem.

Additional reporting by Helen Honour TTA helpline: 0845 6000 993 Teachers Pensions Agency, tel: 01325 745547, www.teacherspensions.co.uk