He told delegates, who earlier had defied the NUT leadership to vote to take on a Labour government over class sizes, league tables and selection: “We won’t tolerate division or bullying or threats, not simply from those who attend union conferences but from anyone who has a vested interest in any part of our country.

“However important they think they are, they will not stand in the way of myself and my colleagues radically changing the education system.”

His speech, which earned a standing ovation from more than half the conference, underlined Labour’s determination to pursue a radical back-to-ba sics agenda for schools in the teeth of opposition from within the profession.

Despite a series of critical speeches from hard-Left delegates which had been scathing about new Labour policies, his comments were warmly received by many in his audience.

In contrast to his last visit to an NUT conference two years ago, when he was jostled after saying poor teachers should be weeded out, he was politely received even by hard-liners. His determination to present a tough image in the face of militant threats was underlined outside the conference when he told journalists he believed teachers should not strike.Withdrawal of labour should only be used as a last resort, he said.

But he said Labour did not support the Conservatives’ plan to outlaw strikes by teachers.

Mr Blunkett departed from his planned speech - circulated in advance to journalists - in which he reiterated his support for teaching children the basics and delaying the use of calculators until later in primary schools.

Instead he delivered a passionate defence of his right to speak up on school standards, with a heart-felt description of the six years he spent at evening classes to take A-levels and a business qualification.

“When my own children went into an inner-city comprehensive with very low academic standards, I determined to liberate the children we represent from past dogmas and fights about the lite succeeding and the rest being written off.” He added:“Anyone who doubts my commitment needs to take me on personally in terms of what they have done and what I have done.’’

It was direct comments like these which won him his standing ovation. He also won loud applause for promising to scrap the nursery voucher scheme, and to cut infant class sizes. And he stated unequivocally: “Class size really does matter.”

In reply, the NUT’s general secretary Doug McAvoy welcomed Labour’s commitment to smaller classes and the scrapping of the nursery voucher scheme but tackled Mr Blunkett’s comments about refusing to be bullied by militants head on: “Industrial action is a resort we will turn to. We will fight to retain that right. It is not bullying and threatening. It is saying we believe in our policies.”

It was left to Don Foster, the Liberal Democrat education spokesman, to criticise Labour policy. “A gimmick a day will keep the Tories at bay,” he told the conference. He was criticising Labour’s announcement this week of a new numeracy task force.

Smaller classes and decent schools to work in were what teachers needed, said Mr Foster, a former NUT member; only then would numeracy and literacy start to rise.