Heads on both sides of the border originally only had until the end of this year to finalise radical changes to staffing.

These include making the controversial switch from management allowances to teaching and learning responsibility (TLR) payments, which is expected to lead eventually to pay cuts for thousands of teachers.

The need for lengthy consultations on the restructuring and the long wait for official guidance had led many heads to fear that the timetable was too tight. This week the Welsh Assembly extended the deadline for staffing reviews until March 31, 2006. A Welsh Assembly Government spokesperson said its consultation found the December deadline unrealistic, and called for greater flexibility.

The decision came as the Secondary Heads Association, a member of the Rewards and Incentives Group (RIG), which set the original deadline, said it too would now push for an extension in England. It had previously said the timescale was adequate.

Welsh schools will still have to implement their new structures by the end of 2008 and will not be able to award new management allowances after the end of 2005.

They can award temporary management allowances until December 31, which can then be paid for up to a year afterwards.

Chris Keates, NASUWT general secretary, and a member of the RIG, which includes union, government and employer representatives, said the decision was regrettable, would create uncertainty for Welsh staff and might cause widespread disaffection.

But David Hart, general secretary of the National Association of Head Teachers, now outside the RIG, said: “This is the right decision; three months will make all the difference.” He said Ruth Kelly, the Education Secretary, had turned down his calls for an extension period in England.