Headteachers are threatening to boycott the appraisal system that will determine whether teachers can receive performance-related pay.

The decision by delegates at the National Association of Head Teachers annual conference in Cardiff rejects a personal appeal for support from the Prime Minister, Tony Blair, who spoke to them on Wednesday.

Headteachers passed a resolution urging their leaders to advise all 32,000 members not to implement the new appraisal system for performance-related pay in England, unless the government agreed to the union's conditions.

Margaret Morgan said headteachers were worried about "bureaucratic overload"

The union wants assurances that pay will not be linked directly to pupils' achievements in exams and tests; that any performance pay structure will be adequately funded and that it will not create an excessive administrative workload.

The union's General Secretary, David Hart, said the conditions - delivered to ministers in March - were a minimum requirement and were "not to be negotiated".

The resolution was proposed by Margaret Morgan, who said consultation meetings with union members had given a clear message that headteachers regarded the new appraisals as involving "bureaucratic overload" and "an impossible timescale".

"Without the consent and the willing and fruitful labour of the heads and deputies in this country the proposals ¿ have absolutely no chance of success," she said.

The proposals are a central plank of the government's Green Paper consultation document on reforming teachers' pay and conditions.

The pay reforms would deliver an immediate £2,000 salary boost to teachers on the top of the present pay scale - approximately £23,000 - if they chose to go through a 'threshold' onto the new system.

There would be the possibility of further increases, up to a salary of about £30,000, depending on successful annual appraisals.

During the debate, Jim Price, head of South View CP School, Crowland, Lincolnshire, argued that the union was not being robust enough in its opposition to the Green Paper.

Raising the status

"Just as we don't expect something for nothing, nor should the government expect something for nothing from us," he said, in a reference to Tony Blair's speech.

"Yesterday we were told the government wanted to raise the status of teachers to that of lawyers or doctors. Few in this room would disagree with that if the pay came with it."

Joy Millar, head of Earlswood Infants and Nursery School, Surrey, also wanted tougher opposition.

In her school, almost all the teaching staff were members of the National Union of Teachers - which next week begins a boycott of all appraisals. Even if the NAHT's conditions were met, she could not see herself trying to force those teachers to take part in appraisals, she said.

Another headteacher, David Gray, said that as well as being the head he also taught in his school, Babbacombe Primary, Devon. Managing the appraisal system would take him out of the classroom and the children would suffer as a consequence, he said.

'Reasonable' conditions

"The major thing about this is, if it's not put in properly, the children are going to suffer, as well as colleagues' morale in the staffroom," he said.

Speaking after the vote, Mr Hart said the union's conditions were a mixture of "manageability" - such as funding and the amount of bureaucracy - and matters of principle, such as an opposition to a link between pay and pupils' exam and test results.

They were reasonable and could be met by the government, he said.

"I speak to senior executives in the private sector and those charged with implementing performance-related pay in the Civil Service, and they all express reservations about how it is operating - they all say it takes a long time to settle down," he said.

He said his members were in favour of performance management, they believed that there did have to be change in education, but what they wanted was a system that would work - and they did not think the government had got it right.

"Heads and deputies are not going to be conned by anybody into accepting a package which they do not feel is manageable," he said.