FEARS were growing today that the teaching shortage could mean up to 6,000 sub-standard teachers taking classes when the autumn term begins next week.

Heads felt that a fifth of the appointments they made this summer were unsatisfactory, according to a poll by the Times Educational Supplement and the Secondary Heads Association.

It said that there could be 5,000 vacancies left - despite the fact that schools have been forced to take on so many second-grade applicants - on the day when one report claimed teaching has become an "unsustainable profession".

The research, by think-tank Demos for the National Union of Teachers, said the current shortage crisis will only be reversed if working conditions improve.

The TES/SHA poll covered 7,127 appointments at 827 comprehensives.

Headteachers said they were unhappy with the calibre of 1,372 of the successful applicants which, if replicated across England and Wales, would mean there were 6,000 unsatisfactory teachers working in state schools out of 30,000 new appointments.

That finding echoed the infamous remark by Chris Woodhead, former chief inspector of education watchdog Ofsted, who aroused the hate of the unions in 1996 when he claimed there were 15,000 incompetent teachers.

The TES/SHA survey came out just after Mr Woodhead's successor, Mike Tomlinson, warned that shortages were the worst they had been for 36 years, and said 40 per cent of younger teachers were leaving within three years of qualifying.

SHA general secretary John Dunford said: "5,000 vacancies and numerous unsatisfactory appointments will make the coming term very difficult for many schools.

"This is certain to affect the capacity of schools to continue to raise standards."

At one South East comprehensive, the head took on two teachers who "walked in off the street with no qualifications", the survey found.

The regional breakdown showed that in the West Midlands, 703 appointments had been made, with 19 per cent of appointees deemed unsatisfactory. Unfilled vacancies totalled 106.

Meanwhile, the Demos report said the Government's attempts to create a world-class education system were being undermined by the fact that the profession's morale had plummeted.

NUT general secretary Doug McAvoy predicted that schools would be forced on to four-day weeks in the autumn term.

Meanwhile, international development charity VSO said teachers were being "looted" from developing countries such as India to fill Britain's schools.

The domestic shortage paled in comparison with those afflicting countries including India, South Africa, Namibia and Nigeria, it said.