The authority's pension deficit has nearly quadrupled since March 2007 - when it stood at £158 million - leading to fears that its employer contributions to the fund will have to be drastically increased.

A report from the council's corporate finance manager, Peter Edwards, said its funding level in September stood at 68 per cent of the total liability - more than it had been in June, but still less than the March 2007 level of 89 per cent.

The pension fund has plunged further into the red over the last two years as a result of the worsening economy.

But according to Mr Edwards, the fund's estimated liabilities - the amount it would have to pay out if all employees retired now - rose by 30 per cent between March 2007 and September 2009.

The council now fears that unless the economy recovers rapidly, it could have to increase its employer contributions from 19 per cent of its wages bill to 31.4 per cent.

The fund is next due to be valuated in March.