A quarter of a million qualified teachers are not working at the chalkface, official Government statistics have revealed this week.
About 255,000 people who have passed through the training process have chosen not to work in the classroom. Of these, 88,000 never even entered the profession.
The Department for Children, Schools and Families' statistics show there is one qualified but non-working teacher for every two who currently do the job in England. The bulk of these have trained to work in secondary schools - 134,000 compared with 81,500 in primaries and 6,300 in special schools and pupil referral units.
The group is significantly skewed towards an older demographic. More than 130,000 teachers in the 50-to-retirement age bracket are not teaching, while about 11,900 people who qualified before the age of 29 have never worked as a teacher.
According to John Bangs, head of education at the NUT, the solution to teacher supply issues is to solve long-running problems teachers have with their job. He said the various quangos charged with overseeing education often unintentionally sabotage each other's work.
"It's clear many headteachers leave because they don't want to face another Ofsted inspection," he said. "This is one example of a lack of joined up thinking when you have the National College working to keep them in their posts. Top-down pressure on schools is still too much, and this is creating major issues in the job market."
The stats also show that retirement of heads again rose this year, but not to the extent that some had predicted. They have been going up every year since 198990, from 8,500 retired to 19,190 last year. But a big increase has not materialised this year.
John Dunford, general secretary of the Association of School and College Leaders, believes the "retirement bubble" hasn't yet burst.
"It's estimated school leaders will be leaving their jobs in droves, but the expected increase didn't seem to start this year," he said. "There's anxiety that we have merely postponed the issue. Succession planning and the National Professional Qualification for Headship have increased the supply, but now we've got to bring those people into the job. We've got to make it more do-able".
'I never thought I would end up doing this'
Garth Buckle considers himself a teacher - even though he has not taught in the conventional sense for two decades. The business links team co-ordinator at Hounslow Education Business Partnership, Middlesex, sets up work experience and organises talks for hundreds of youngsters. He moved outside of the classroom in the mid 1980s.
"My background as a teacher is enormously helpful," he said. "I'm still in the world of education and I'm still teaching as such. As a teacher I used to get colleagues from the community to come in to assemblies and lessons and I became interested in getting them more involved with schools"
Mr Buckle started his career in Heston Community School in 1971, and taught there for 15 years. He became interested in involving the community and parents in schools and took a diploma in the principles and practice of commerce at St Mary's College in Twickenham in 1983 before founding the business partnership a few years later.
"I never thought I would end up doing this when I joined the profession, but the job is all about helping children and I'm still doing that," said Mr Buckle, who was given an MBE last year for his services to young people.