Both candidates oppose “pay-by-results”. But challenger Kevin Courtney says incumbent Steve Sinnott has failed to get the union leadership to mount a campaign.

Ministers will soon unveil details of how the scheme will work and outline this year’s pay rise, expected to be an inflation-busting rise of 3 to 3.5 per cent.

The School Teacher Review Body’s report is due to be delivered to ministers next week. It will detail the pay scales which will allow classroom teachers to earn up to pound;35,000 a year but which would be related to annual appraisals linked to pupils’ progress.

Mr Courtney, a member of the Socialist Teachers’ Alliance and co-ordinator of School Teachers Opposed to Performance Pay, said:“We both say we are opposed to performance-related pay, but I’m saying up front we must do something about it.”

In an informal ballot organised by STOPP to put pressure on union leaders, teachers in Lewisham and Liverpool backed a one-day strike.

But Mr Sinnott warned a victory for the Left would divide the profession. “We are the only union to have balloted members and taken industrial action over PRP.”

Union leaders unanimously condemned the expected pay rise, saying it would do nothing to lure graduates into the profession.

But local government leaders have told Education Secretary David Blunkett an extra pound;150 million will be needed to meet the settlement, warning that class sizes would rise without it. Graham Lane, education chairman of the Local Government Association said: “Authorities will not be able to fund their part of the cost.”