As the holidays began, schools minister Stephen Timms was in defiant mood. “We’ll have the teachers we need by September,” he predicted. Headteachers, gloomily cancelling late August plans in the expectation of long days on the telephone or - worse - the timetable, were unconvinced. Recruitment consultant John Howson called it “a terrifying situation”. The minister, though, was unrepentant. “I’m certainly not being complacent,” he said. “There’s a great deal of work going on at the moment to fill those vacancies.”

He was referring to the latest project to boost recruitment, the Government’s heavily advertised Welcome Back scheme, tempting teachers back to the profession. “Those who can, can again,” runs the less than catchy slogan. One of the advertisements features a typical “Sorry you are leaving” card. “Have you got one of these?” the caption says. “It could be worth up to pound;4,000!” The small print spells out the details: if you’re back teaching in a maintained school before December 31, you will get an immediate bonus of pound;500, and pound;1,500 after your first full year - both sums are doubled if you teach a shortage subject. There are also paid training courses if you feel your skills are rusty, and there is no upper age limit.

The hope is that the abyss of vacant posts will be filled from what policy-makers call the PIT - the pool of inactive teachers. It includes all teachers under 65 who have permanently or temporarily left the profession, so women taking a career break are there alongside inspectors and consultants. Its most significant group, though, is the “early retirers”.

And this is a very large group. Between 1990 and 1995 in England and Wales, about 3,500 teachers a year took early retirement on grounds other than ill-health. In 1996 and 1997, as the Government moved to close down this route, the figure leapt to 12,000. Since 1997, with latitude given to LEAs and governors to “restructure” struggling schools, about 2,500 teachers aged between 51 and 60 have retired every year. That’s a lot of teachers.

But are they willing to come back? And will the schools still want them? “It’s harder to come back than people think,” says one head. “They lose confidence. Too much has moved on, too much has changed.” Another head has no such reservations. “Right now, anybody who can stand up in front of a class has got to be a bonus.” A third says: “Yes to both questions. I’ve got a really good one now. His name is Allan BrookI” Allan retired in 1997 at the age of 55 after spending 30 years in one school. He was head of English, the school roll was falling, there were budget problems. When he was offered redundancy with pension enhancement it was too good to miss. To begin with, things weren’t as he expected. “I’d hoped for a part-time job but only got occasional supply days. I was bored. I missed the pupils.”

On impulse, he took a post as learning support assistant at Lawnswood comprehensive in Leeds. “I was working with kids, but there was no marking, no management. It was wonderful. The teachers were brilliant. I learned more about teaching English in one year than in the whole of my previous career. It lit my touchpaper again. I realised that I really wanted to get back into teaching. Now I’m teaching half-time, up to the limit in pension terms (see box), enjoying life again, getting a great buzz.”

Other oldies tell similar tales. Dianna Pettit, for example, is teaching at the newly built Causeway school in Eastbourne. Before retirement she was head of science in a split-site London comprehensive and finding it increasingly stressful: “I had just one admin period a week, I simply couldn’t get everything done.” The turning point came when her husband had an accident; at the age of 53 she stepped down.

She took a one-term maternity post. Then, out of the blue, Causeway telephoned her just days before the school was due to open. Would she stand in as head of science as the teacher who’d been appointed was ill? “I said yes. And it was stressful, of course it was, but it was a different sort of stress. It was exciting, very fulfilling. And after that, the head made me sort of permanent part-time supply. I teach science, some Spanish which I am learning myself, and almost everything else - except IT!” It’s an arrangement that suits Dianna as well as the school. “I like the freedom that supply status gives. I couldn’t be doing a clerking job or arranging flowers full-time. I love the adrenalin. But there has to be give and take.”

Ian Haines lives in Plaistow, east London. He, too, came back “on supply”. Like Allan Brook, he had spent 30 years at the same school - in his case, a London comprehensive. “But for the last year or so, I was making excuses. And I knew the early retirement gate was closing. I packed it in in 1996.” He was 53. After a few months he found that he was missing the children.

So he did some part-time teaching at his local primary school. A brief return (part-time) to secondary work convinced him that primary teaching was more fulfilling. Supply agency Select Education was advertising for primary teachers: he applied, was interviewed and, to his surprise, was taken on. The company put him through the Department for Education’s training courses in literacy, numeracy and ICT, and he hasn’t looked back. So would he recommend it? “Certainly. I used to feel sorry for supply teachers. But I’ve now worked in 21 different primary schools. It’s given me new confidence, new expertise. And the thing is, I can pick and choose. I do two or three days a week; I get pound;100 a day, my pension’s not affected. Of course I recommend it.”

Joe French, who was a secondary deputy head for 18 years in Waltham Abbey, Essex, is another typical returner. In his case, it was the restructuring of the management team that made early retirement possible. “But I wanted to keep my hand in, so I rang round Colchester to say that I was available if wanted. Moulsham high school jumped, offered me three days a week - and I’m thoroughly enjoying it. I prepare my work properly, I’m enthusiastic and energetic, I feel invigorated. All I have to do is think about my teaching. It’s like heaven.”

Bob Wicks, chief executive of Select, is a firm supporter of the Welcome Back campaign. Almost 20 per cent of the teachers on his books, he says, are over 50, and they’re in constant demand. There are, however, reservations. Chris Nicholls, Joe French’s head, says the pension rules, which discriminate between agency-employed returners and those employed by schools or local authorities, should be reviewed.

Equally, schools that take retired teachers back have got to be flexible. It is, after all, a sellers’ market. “I’m a pot of gold,” says one returner. “I can pick and choose.” They also have to give returners targeted support, something Dianna Pettit stresses: “It’s vital that people coming back into teaching have a mentor they can go to. It’s like being an NQT all over again.”

WATCH YOUR PENSION

* Teaching after retirement, whether full or part-time, may be pensionable as long as the employer is a member of the Teachers’ Superannuation Scheme, and as long as the maximum number of contributable years (45) is not exceeded.

* Your existing pension is not otherwise affected by your earnings in post-retirement teaching, unless your annual earnings and pension together exceed your salary at retirement as adjusted for inflation, in which case that year’s pension will be reduced pro rata.

* This pension reduction rule does not apply if you are employed and paid by an agency that is not a member of the Teachers’ Superannuation Scheme.

* For specific advice consult leaflet 192, available from the Teachers’ Pension Agency, Mowden Hall, Darlington DL3 9EE. Tel 01325 392929, or go to www.teachers pensions.co.uk. Alternatively, consult the Welcome Back helpline on 0845 6000 994; website www.canteach.gov.uk