All schools are supposed to publish new staffing structures by the end of December. But The TES has learnt that a panel of heads and teachers set up by the Government to monitor the impact of its policies has said the deadline may be impossible to meet.

Any delay would cause chaos as schools are meant to fund part of the pay rise for experienced teachers, using savings made by replacing management allowances with teaching and learning responsibility payments (TLRs).

It will mean a tough autumn for Ruth Kelly if she survives the general election as Education Secretary, or for David Miliband, touted in government circles as her successor. Next term, heads must also give teachers obligatory non-contact time, which many say they cannot afford.

This week Mick Brookes, who takes over as general secretary of the National Association of Head Teachers in September, called for funding for teachers, not support staff, to cover this planning, preparation and assessment (PPA) time.

The implementation review unit called on Ms Kelly to assess how long it would take the average primary and secondary school to work out how to introduce TLRs.

The new system is meant to be phased in by the end of 2008, but it has already caused controversy because it will mean pay cuts for thousands of teachers.

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