The details are held within a leaked confidential report. It shows how the council has accumulated an unexpected reserve of pound;231,500, which deputy chief executive Julia Evans says should be reduced “in a controlled manner”.

One idea is to plough the cash into reducing teachers’ fees, which are paid for by the Assembly government via local authorities.

This year’s fee of pound;32 from 36,500 teachers is the council’s key source of income. Based on current figures, this is expected to rise to pound;37 next year and pound;38 in 2008-9.

Alternatively, this could be held at pound;35 in both years by using the extra cash, but this would breach a council rule that income should meet expenditure. This would also lead to greater increases to the registration fee in later years.

An alternative is to buy property. The council spends about pound;80,000 a year renting its Cardiff headquarters. There is also a third option of holding the cash to fund future planned developments.

NUT Cymru called for the cash to be ploughed into professional development.

“We are concerned that the money available for supply cover when teachers go on courses is insufficient,” said communications officer Rhys Williams.

“It seems the GTCW should be rather more generous.”

But Geraint Davies, secretary of teachers’ union the NASUWT Cymru, said:

“Teachers will be aghast to find the GTCW has accumulated such large reserves in such a short time. It seems that the council has been overcharging since its inception five years ago.”