Supply teachers now account for more than one in 10 of all teachers registered with the General Teaching Council for England (GTC). In the past year, their numbers have increased by more than 17,000, a rise of more than 50 per cent in just one year. Whether there is enough work for the 51,000 supply teachers registered with the GTC is a moot point. The more interesting question is where have these extra teachers come from?

Some could be NQTs who cannot find a teaching post, but the numbers of newly qualified teachers in service and designated as a supply teacher has barely altered from last year at 2,713. This leaves 48,000 other supply teachers registered as in service but presumably, not necessarily, in work. Perhaps this is the first sign of the effect of the recession on the labour market for teachers.

Are these former teachers, now unemployed, who have re-registered with the GTC or are they potential returners anxious to have a registration in place so that if they did lose their job they could apply for a teaching post straightaway? Sadly, the figures don’t tell us the answer. But, 5,000 are over 60, so some are teachers who don’t want to retire, or need the income. A further 15,000 are between 25 and 39, and these teachers might represent career returners seeking work.

How much supply work there is for these additional teachers isn’t clear. But, with the new rules from this September, pickings may be thinner than in the past unless the swine flu epidemic creates an unexpected demand for replacement teachers.

• John Howson is a director of Education Data Surveys, part of TSL Education.