Mainstream schools have snubbed Michael Gove's call to swap qualified teachers for moonlighting jobbers, with just one in 40 teachers traded.

The National Union of Teachers (NUT) claimed a victory against the Education Secretary after figures released under the Freedom of Information Act showed "encouraging" resistance to the coalition policy.

The free school scheme, which bankrolls new privately run schools, has suffered harsh criticism from community groups and teaching unions.

The schools, which still account for just 1 per cent of England's primaries, are not required to follow the national curriculum or employ qualified teachers.

Mr Gove's Department for Education has vigorously defended the policy, saying it offers "additional flexibility" for employers.

But while the policy is now in its third year, school heads themselves appeared reluctant in yesterday's figures.

Of 80 mainstream free schools surveyed, just 26 of their 1,029 teachers did not hold qualified teacher status.

NUT deputy general secretary Kevin Courtney said it was "encouraging" to see free schools backing the union's position.

"Children and young people deserve to be taught by a qualified teacher," he said.

"Being an enthusiastic amateur does not in any way substitute for the skills and knowledge of child development gained with qualified teacher status."

But some free schools were found to rely almost entirely on untrained staff at the whiteboard.

At Trinity School in Sevenoaks, Kent, just two of its nine teachers were qualified.

This month Department for Education officials slated West Sussex's failing Discovery New School for closure, barely two years after it opened.

Just two of its seven teachers had qualified teacher status, according to yesterday's release.

Mr Courtney said the lesson was clear - free schools were free to abuse the policy by skimping on higher-paid trained teachers.

"Teaching is a profession, and like any other profession it needs to be mastered," he said.

Association of Teachers and Lecturers general secretary Mary Bousted said the figures demonstrated the erratic nature of Mr Gove's project.

"We don't think unqualified people should be teaching," she said.

"It's important that they understand that children develop and learn in different ways and at different rates."

A Department for Education spokesman said the figures made no difference.

"It is entirely up to head teachers who they employ and we trust their judgement in getting the mix right for the pupils they know best," he said.

The figures follow last week's warning that up to half the teachers in England and Wales this year have considered quitting altogether.

A ComRes survey of more than 500 teachers commissioned by fellow teachers' union NASUWT found 52 per cent had "seriously considered" leaving their current job in the last 12 months, while 47 per cent had mulled giving up teaching entirely.

Those polled overwhelmingly blamed workloads, with 79 per cent describing it as their biggest worry and 86 per cent saying their workload had grown still larger in the past year.