Schools will get three extra months, until January 31, to introduce changes to performance management that will give line managers and heads of department a key role in determining pay rises.

Nigel Middleton, director of the Head Support consultancy, said fewer teachers would get pay rises because schools would tighten the criteria for progression up the pay spine. Heads would have to prove to Ofsted that higher salaries only go to the best teachers.

A letter from the Department of Education and Skills said the proposals were delayed due to consultation with local authorities which showed not all schools would be ready for the changes by autumn.

But the NUT claimed victory after threatening the DfES with judicial review after being excluded from initial negotiations about the changes.

The union said ministers breached their legal obligation to consult teachers’ representatives by consulting the rewards and incentives group (RIG), which includes the NASUWT, Association of Teachers and Lecturers, Professional Association of Teachers and Association of School and College Leaders, but not the NUT or National Association of Head Teachers. The RIG unions have backed the changes and said a new three-hour limit on classroom observation for performance management purposes was “a great victory for teachers”.

Of line managers recommending pay rises, the NUT said : “This could have a profound and damaging effect on the collegiate professional relationships of teachers.”

The consultation period has been extended until August 30. The NUT is waiting for a formal response to its threat of judicial review before deciding on any further action.