Sussex Police are sitting on a "rainy day" fund of more than £10 million - enough to pay for 200 extra officers a year.

The cash is earning interest in Sussex Police Authority's bank account even though it has hiked council tax for county householders every year since 1997.

Forces are advised to keep an emergency reserve of about two per cent of their annual budget, which was £257,669,000 last year in Sussex.

But Sussex Police are sitting on £10.1 million, according to Government figures, which is four per cent of their 2004/5 budget.

An officer costs an average of £50,000 to put on the beat - a figure comprising the £31,450 average salary, plus training, support and pension costs. Nationally, police have £950 million sitting in the bank, enough to pay for 19,000 officers.

Shadow Home Secretary David Davis said: "At the moment we have a situation where hundreds of millions of pounds have not been spent.

"If we want to reverse Britain's trend of rising crime we need to use this money to put more officers on the beat."

Figures, released by Police Minister Hazel Blears, revealed that the Metropolitan Police tops the "rainy day fund" table with £186 million, or 6.7 per cent.

A Home Office spokesman said the reserve was an operational decision for individual forces. The Audit Commission suggested at least two per cent. The Association of Chief Police Officers said forces had to keep money in reserve in case of unexpected pressures, such as a big murder inquiry.

A Sussex Police Authority spokesman said: "Half of the £10.1m needs to be reserved so there is no question of being able to fund an extra 200 police.

"Additionally this is a one-off resource and cannot fund ongoing commitments so 200 extra officers would need £10m each and every year - the equivalent of a 15 per cent increase in council tax."