The biggest teachers' union has set itself on a collision course with the government and its own leadership by calling for a strike ballot over performance-related pay in England and Wales.

Result of final vote

For strike: 105,208 Against: 82,114 Majority: 23,094

The National Union of Teachers' own general secretary, Doug McAvoy, who has campaigned against a protest strike, said "parents would be appalled by the decision" and would be "unable to understand it".

The Education Secretary, David Blunkett, has attacked the strike threat from the NUT's annual conference as "the first time in history that a union conference has voted for strike action when offered a pay rise for simply doing their jobs well".

And even if a one-day strike went ahead, the education secretary said it would make "absolutely no difference" to the government's plans.

But Mr McAvoy claimed that it was unlikely that teachers would vote in support of a strike.

And despite the conference's decision, he said he would refuse to campaign in support of a "yes" vote in the strike ballot.

He suggested that there would have to be a preliminary "indicative" ballot - which would further stall a vote of the whole membership.

Work to rule

The conference vote for a strike ballot, which followed a bad-tempered debate strung out over four days, was won by 105,208 to 82,114 - raising the prospect of the first all-out teachers' strike for a generation.

The motion agreed by the conference commits the union to call a ballot for a one-day protest strike at the earliest opportunity - as well as launching a work to rule which would see teachers boycotting out-of-school and voluntary activities.

But in his end-of-conference speech, Mr McAvoy rejected strike calls as "pre-determined political posturing" and unrepresentative of teachers wanting a practical campaign of resistance to performance pay.

He was speaking as delegates waited to hear the result of the vote on the strike ballot - and with thunder rumbling outside the conference hall in Harrogate, North Yorkshire.

Mr McAvoy said there was no clear majority within the union for strike action and most teachers would not support a protest strike in the summer term.

'Few alternatives'

"Believing propaganda you know to be false leads to dishonesty," said Mr McAvoy, who accused the left wing in his union of fooling itself that support existed for a strike.

Setting himself against the decision of conference, he declared: "I will not be party to conning members."

But those in support of a strike ballot had argued that they were left with few alternatives in their campaign to block performance pay for teachers.

Bob Sulatycki, a delegate representing Kensington and Chelsea, said: "The alternative to a strike is to put up the white flag".

And John Lockwood, representing Mid-Warwickshire, said the union had "reached a point where we have to decide whether to accommodate performance related pay or stand and fight it."

He said the union's leadership was "mesmerised by the Labour government" and needed to assert its independence.

Tom Denholm argued that a local survey in Newcastle had revealed only 20% of NUT member likely to support a strike, but other delegates pointed to the union's survey of all its members, which had found 59% in favour of a one-day strike.

As the NUT conference ended, that of the second biggest teachers' union, the National Association of Schoolmasters Union of Women Teachers, was getting into full swing in Llandudno.

Its general secretary, Nigel de Gruchy, accused the NUT conference of sullying the image of the teaching profession by its actions.