Britain’s second largest teachers’ union threatened to ballot for industrial action if ministers attempted to scupper national pay and conditions or change the criteria for progress on the upper pay spine.

Delegates were told that the powers to deregulate pay and conditions, contained in the Education Act 2002, represented the top of a “slippery slope”.

Roger Kirk, executive member, said: “Teachers working in the system expect, in broad terms, to do the same job wherever they are in the country.

“If you do the same job, you get the same pay and the same conditions of service. That has been the principle for the past 100 years, and that is the principle we need to cling to.”

The conference voted by an overwhelming majority to take all measures necessary, up to and including strike action, if any school or local education authority attempted to use the new powers.

Mr Kirk said: “The big worry is Gordon Brown’s clear perception that regional pay is the way forward for the whole of the country.”

On the upper pay spine action, Eamonn O’Kane, NASUWT general secretary, said it seemed likely that the Government would attempt to make the progression criteria tougher within the next year. He said teachers could fight back by refusing to carry out performance management.

The threats came at the end of a week in which delegates also voted in favour of industrial action against schools which failed to implement all aspects of the national workload agreement.

Mr O’Kane said he had enjoyed his first conference as general secretary, but admitted, somewhat euphemistically, to a few “hiccups”.

Earlier in the week, members had voted against plans to investigate the possibility of a merged teachers’ union, crushing hopes of a “super union”, a plan Mr O’Kane is known to favour.

Hank Roberts, a member of all three main classroom unions and founder of Professional Unity 2000, said: “It’s a tragedy that disunity has broken out.”

But there was a positive response towards the workload deal which the leadership has signed with the Government, with only two members voting against it.

And delegates pushed for further progress, voting through an amendment demanding a 35-hour week by 2006.

One of the few voices of caution was Ged Griffin-Keane, a teacher from Surrey, who said he feared that his professional status would be lost if teaching assistants were given an enhanced role.

“This is the NASUWT, not the NASUWTA,” he said. “We are voting to de-skill this profession.”