MPs have been reluctant to attack the chief inspector after a series of allegations about his private life, but 16 have now signed an early day motion demanding Mr Woodhead's immediate resignation.
Mr Foster argued that the allegations, which stem from an affair Mr Woodhead had with a young woman, meant the chief inspector was no longer able to do his job effectively.
His remarks show that ministers' efforts to put an end to the debate about Mr Woodhead's future have failed. David Blunkett, the Secretary of State for Education, tried to draw a line under the controversy last week when he said in a written parliamentary answer that there was no evidence Mr Woodhead started the affair with Amanda Johnston while she was still a sixth-form pupil at the school where he taught.
Reports about the chief inspector's private life first surfaced more than two months ago when The Independent revealed Mr Woodhead had told a student audience that relationships between sixth formers and teachers could be "educative and experiential".
Mr Woodhead says that he and Ms Johnston started a nine-year affair after they left Gordano School in Bristol in the 1970s. However, Cathy Woodhead, the chief inspector's former wife, says he is lying and the affair began while Ms Johnston was still a pupil at the school.
Mr Foster told BBC Radio Four's Today programme that Mr Woodhead was "a failing chief inspector". Mr Blunkett, was a kind man, he said, but the time had come to sack Mr Woodhead. Alternatively, the chief inspector "should have the decency to offer his resignation".
Tomorrow, head teachers' leaders will meet to consider referring to the Director of Public Prosecutions allegations that Mr Woodhead lied under oath about the affair. David Hart, the general secretary of the National Association of Head Teachers, is putting forward the proposal because he believes the Government is trying to "sweep the matter under the carpet".
Mr Foster accepted Mr Woodhead's enemies were out to "get" him, but said that he would never have appointed him - on educational grounds. He said: "He [David Blunkett] should sack him. Or indeed, the proper thing that should happen is that Chris Woodhead should have the decency to resign."
t Fifty-three per cent of adults want more grammar schools, according to an NOP poll published yesterday. But there is a clear split between the generations, with only 44 per cent of under-35s supporting the proposition compared with 68 per cent of over-55s.Reuse content