Hundreds of teachers will find themselves paying the same rate of tax as a top barrister, because delays in receiving their threshold payments will push them into the highest income bracket next year.
Many experienced teachers who met threshold targets are already receiving the extra pay, backdated to last September. On its own, the threshold pay is not enough to trigger the 40 per cent rate of tax.
But because of delays caused by external assessor shortages, others will receive extra payments in the new tax year, starting in April. The backdated lump sum could then push them into the 40 per cent tax bracket when added to next year's threshold payments. Teachers working in London or with management responsibilities are those likely to be affected. Most will already have to pay around pound;256 tax on this year's threshold award but the delays could increase this to as much as pound;467.
Ray Beer, head of sixth form at Norton Knatchbull boys' grammar school in Ashford, Kent, believes a number of middle-managers could be affected: "Our assesor is not due in until March. Just because they can't get people in on time, teachers could be getting different amounts of money. It's iniquitous."
Teachers seconded to education authorities, for example in special needs, are more likely to face threshold delays because assessors are concentrating on schools.
A spokesman for the Inland Revenue confirmed that "generally, people will be taxed in the year they received the income". In the current financial year, the 40 per cent rate kicks in when income exceeds pound;28,400, after taking into account pension, personal and other allowances.
In a bid to speed-up the process, external assessors will receive a pay rise of nearly 30 per cent from March, at a cost of between pound;600,000 and pound;800,000.
An assessor in a school with up to three threshold applicants will see fees rise from pound;260 to pound;342.
A Department for Education and Employment spokesman said: "Local education authorities can pay out the funds as soon as the head teacher notifies them about results of the school's assessment. Of course, this would not have arisen had the National Union of Teachers not forced a delay with its court case."