Complaints have been made to David Blunkett, Education Secretary, that the Government is already preparing contracts for external assessors who would judge whether teachers pass the threshold for performance pay.

The second largest teaching union, the National Association of Schoolmasters Union of Women Teachers, has warned Mr Blunkett that the consultation could be hopelessly compromised if he presses ahead before the end of statutory consultation. Nigel de Gruchy, general secretary, said in a letter to Mr Blunkett: “It seems the desire of the Government to push things forward could lead to some difficult circumstances.”

The Government plans to start assessing teachers for the threshold - there are 250,000 teachers at point 9 on the pay scale who are eligible - from January.

The pay increase would take effect from September. Successful teachers would get a pound;2,000 rise and move to a performance-related scale.

The proposals, outlined in a Green Paper earlier this year, are being processed by the teachers’ pay review body, but Mr de Gruchy is concerned the Department for Education and Employment is pre-empting its decisions. He said the union would be seeking legal advice, and was also worried by the tight timetable.

The DFEE has told the review body that its evidence, which will include the Green Paper proposals, will not be available until the end of September. The review body is then expected to publish its report in the new year.

Bill Herron, assistant general secretary, said: “We have warned the Secretary of State this process is too important to be rushed. The Government is in danger of getting structures wrong if the consultation is too speedy.”

A DFEE spokesman said there had already been a long and full consultation on the Green Paper.