It was in the end the most public of apologies. Standing ovations by both platform and rank and file delegates and spontaneous applause greeted the man who had been jostled and jeered by an angry mob at the National Union of Teachers’ conference.

As newspaper headlines screamed condemnation for the attack on David Blunkett, Labour’s education spokesman, the National Association of Schoolmasters Union of Women Teachers sought to make amends.

The warmth of his reception was almost rapturous. It prompted Mr Blunkett to remark: “You are such a wonderful audience. And you are listening!” That it generated brownie points for the NASUWT as the National Union of Teachers struggled against the challenge from left-wing extremists did not go unmissed.

Never one to shy away from publicity, Nigel de Gruchy, union general secretary, swiftly pointed out the “polite, warm way” in which Mr Blunkett was welcomed, “in the same way that we welcomed Gillian Shephard”.

“I hope that the image of the profession has at least been restored and that the public can see that the majority of teachers are capable of receiving politicians from the two main political parties in a civilised fashion, ” he said.

Whether the damage limitation has been successful or not remains to be seen, and will be largely dependent on action that the unions take to combat rising class sizes.

David Blunkett warned the NASUWT, which will strike as a last resort, that parental support built up in the campaign over cuts could be jeopardised by industrial action by teachers.

“Whatever you do, don’t do it out of frustration and anger in a way that affects my children’s education, your children and the ones you teach. You won’t get satisfaction and will turn against us those who are currently with us,” he said. “Don’t do anything now that will in any way upset the commitment we have and which will lead to parents being alienated.”

Mr Blunkett said that restoring discipline and teaching children about rights and responsibilities so that they left school as socially responsible adults were essential for securing change.

He laid the blame for rising class sizes at the door of the Government for refusing to fund fully the 2.7 per cent pay rise for teachers and pledged a decade of investment in education from a Labour Government. To the delight of delegates, he referred ironically to an oft-repeated view on education held by Gillian Shephard, saying: “It isn’t something we need to invest in and when we get the economy back on its feet, it is something to invest in and support in order to put the economy back on its feet.”

Both Gillian Shephard and David Blunkett abandoned their prepared text to speak to union members and appeal against direct action.

Outside the conference hall delegates praised Mrs Shephard as an accomplished speaker, but one who had given them little substance. Mr Blunkett made them feel good not only because they could apologise on behalf of the profession but because he made them feel valued and important.

“I am on your side because you are on the side of children and parents, of a decent education for all children. We are united behind the same banner. Every child needs to be a star with every teacher there to help that child flourish. ”

With term starting this week, the prospect of redundancies and widespread cuts, they were words destined to go down well.

Delegates from Kent predicted that if action on class sizes went ahead it would not be histrionic but measured and controlled, based on workload and worsening conditions of service.

In a theme not unlike that taken up by Mr Blunkett, but raised the day before his conference speech, one delegate said: “Every child is precious, a diamond which needs to be polished. It is very difficult to do that in a large class. You need a situation in which you can see the pupil’s needs. If you are overburdened that can prove difficult.”

A colleague added: “People who utter these things about class size not mattering are talking about an education system they experienced 30 to 50 years ago which is totally different to the world of education in the 1990s.”

Julian Chapman from Gloucestershire, where primary classes can be as large as 38 pupils, said: “I hope that reason will prevail and that we might not have to do too much in terms of disruptive action.

“It is inevitable that some parents will question the action but I still feel that most parents believe that short term-loss of schooling is a small price to pay to stop the long-term deterioration in the education of their children. ”

With attention focused on the battle over class sizes, the fight over workload went largely unnoticed. But the NASUWT, which led the boycott on national curriculum testing and assessment, is preparing action on the issue.

Delegates attacked initiatives such as records of achievement, the special needs’ code of practice, GNVQs, the growth of school and college developmental plans with their associated working parties and briefing papers, as creating an even greater workload than testing and assessment.

Unanimously they backed a motion instructing their leaders to take whatever action necessary - including boycotts - to safeguard members.