“We didn’t actually manhandle Mr Blunkett,” the Socialist Workers’ Party member told The TES. “I was merely expressing my democratic right to be angry.” Ms Crowhurst, a delegate at the conference who teaches at a school in Lewisham, said the trigger had been Mr Blunkett’s reported comments at the ATL conference last week. “I want a Labour government, but I don’t want the Labour party to be making statements about sacking teachers. Mr Blunkett has suggested that teachers are the problem, not the Government.”

Most delegates at the Blackpool conference were anxious to echo general secretary Doug McAvoy and the union’s new president, John Bills, in condemning both the intimidation and the damage to the image of the profession - one said that seeing Mr Blunkett pursued into the hall had made him feel physically sick - but that was where consensus finished.

Otherwise, it was as if open season had been declared on the NUT executive’s “real agenda”, its relationship with the Labour party and on Labour’s education policy. Doug McAvoy was undoubtedly right when he said that the SWP demonstrators were unrepresentative of the NUT as a whole, but frustration over class size and the pay award were boiling to the surface at this conference.

Tension began to build on Saturday morning. While condemning the Tories, the incoming president’s speech to conference also included an uncompromising criticism of the Labour leader: “When Tony Blair took the decision to send his son to a grant-maintained school he may well have made some potential converts feel less threatened by the prospects of a Labour government, but he could not have understood just how much upset and dismay that decision would cause throughout the teaching profession.”

As the conference went on to debate Section 11 funding and anti-racism, resentment was being expressed (and fostered) outside the debating chamber because Mr Blunkett had been invited to speak at a “secret” - that is invitation-only - meeting in the evening.

Earlier, at a (poorly attended) lunchtime meeting, Labour’s education whip, Estelle Morris, made a spirited effort to underscore the difference between Labour and Tory education policy and to reassure teachers that Mr Blunkett had not meant to imply a punitive approach to failing schools when he mooted his Fresh Start idea at the ATL conference. All schools, including GM schools, she told The TES afterwards, “will be brought into a totally new partnership with the LEA, an arrangement never seen before. The backcloth behind education will be completely different because we don’t hate teachers, we value them.” She was joined by Labour spokesman Peter Kilfoyle, who reiterated Tony Blair’s promise to make education “the passion of the next Labour government” - “I wouldn’t do the job unless I thought he meant it.”

The speed with which the demonstrators descended on Mr Blunkett when he arrived, shouting “Sack the Tories, not the teachers” and “out, out, opting out” was frightening. Stewards hustled him into a tiny office, pursued by cameramen and protestors, then banged on the door and demanded that he come out. Doug McAvoy told journalists afterwards that it was “a sad day for the union. The image of the mob downstairs . . . will live with me for a long time.”

Mr Blunkett was given a standing ovation when he eventually arrived at the meeting, at which he emphasised that there would be no hard feelings just because “a tiny handful of people have made fools of themselves. There are no differences between the NUT and the front bench of the Labour party. Our relationship is one of mutual respect . . . it’s been a funny week; I say I believe in high standards and people say I’m to the right of the Tory party . . . I’m not offering a threat to schools, but a revolution that lifts standards. ”

He said he sympathised with teachers’ anger about Gillian Shephard’s promise of more money next year - “having raided a child’s piggy bank, they pretend they’re giving the child a present” - but warned teachers to “take care about the action you take to demonstrate your anger . . . action should draw attention to the crisis, but not damage relations with parents.” Regarding selection, he ridiculed the idea that by concentrating excellence on the few, the wealth they eventually create will trickle down to the rest: “A kind of aristocratic incontinence, perhaps?” It was noticed, however, that he left out a paragraph in the speech (released to journalists earlier) on “blocking entry to those living near a school or those who form part of the school’s religious catchment area in order to give preference to those chosen on the basis of selection”.

This could have been construed as an attack on Tony Blair’s decision to send his son to a GM school eight miles from his house.

When Colin Tarrant, executive member for Derbyshire and Nottingham, arrived at a fringe meeting that evening, he refused to speak when he saw some of the demonstrators. “You’ve ruined a year’s work,” he said. “I’ve been a member for 30 years, but today I’m ashamed to be part of the union because of the disgraceful, despicable behaviour of some of the people in it.” He also said that the demonstration was “a set-up”. After the meeting, Sheila McGregor, who had spoken at the conference as well as being involved in the protest, denied this: “It was completely spontaneous. People were angry hearing Tory policies dressed up as Labour. The national executive is out of touch, especially now that we’re in the run-up to the election.”

Asked whether the demonstration had damaged public perception of the teachers’ case, Fran Crowhurst said: “We can’t be controlled by what the Tory media thinks - if you use that logic you’ll never get a Labour government.”

On Sunday morning, the executive lost a crucial amendment to the motion on class size, and conference business was delayed while a card vote was taken on whether to suspend standing orders to discuss the Blunkett incident.