When it comes to filling classroom vacancies, few headteachers would willingly consider anyone other than a qualified teacher. But faced with the current recruitment crisis, many heads are having to use considerable ingenuity to find them. Some are travelling overseas to seek them out, while others find they must look at unqualified alternatives.

The law is hazy on this point, but it is generally understood that heads must employ properly qualified teachers if possible. If this isn’t possible, certain legalities must be considered.

“It is not a legal requirement that classes must be taught by a qualified teacher,” says David Hart of the National Association of Head Teachers, “but the head must be satisfied that pupils are properly supervised in terms of health and safety, and that they receive a decent standard of education.”

Schools usually turn first to supply agencies to fill vacancies, but there can be problems here if the school’s budget is already pushed. Some schools deliberately employ more part-time staff - as learning assistants, for example - who can then stand in when needed as a cheaper form of supply teacher.

Meanwhile, supply agencies are looking overseas for teachers. Some schools persuade overseas supply teachers to stay on as full-time staff, but few of them want to stay in this country for more than a few years.

Some heads actually go as far as jumping on a plane to find teachers, says Bob Carstairs of the Secondary Heads Association - by setting up in a Johannesburg market stall, for example. Overseas teachers can also be found through organisations abroad or via advertisements in foreign newspapers.

Closer to home, one head recently set up shop outside his local supermarket, hoping to attract mothers of four to six-year-olds who might be former teachers considering a return to work. Sending out a “round robin” letter to parents may also produce good results.

Judith Grylls, head of Osmani Primary School in Tower Hamlets, London, says that recruiting newly qualified teachers from the local authority pool has made a difference. “You have to put a lot of work into them, but they usually stay longer than overseas teachers,” she says.

The Government’s graduate teacher programme has been seized on by some schools as a source of new teachers - for instance, people who want to change career but can’t afford a year out of work to do a PGCE. But the GTP is overstretched; with 1,600 applications this term for only 1,000 places, good candidates will be turned away.

“The Government is not expanding this programme as much as we’d like them to,” says Bob Carstairs.

If schools still can’t fill vacancies, and no amount of rejigging the timetable and teaching in larger groups can solve the problem, they may have to consider the legally permissible option of non-qualified “instructors”. Not surprisingly, the number of instructors is rising quite markedly.

“If you can be satisfied that they are able to exercise appropriate discipline in the classroom, it may well be that you can find someone who can fill the gap,” says David Hart at the NAHT.

People with training experience in science or industry can be very useful here, and schools need to make the most of their local business links.

Schools in Portsmouth, for instance, are already looking to their large pool of ex-servicemen and women to provide classroom cover, despite serious misgivings on the part of teacher unions. These “study supervisors” are under the charge of a senior member of staff, and the work that they supervise is set by heads of department.