Statistics from the Home Office show that in 1998, the county spent around £2 million on extra police hours, soaring to just under £5 million nine years later.

City MP Stewart Jackson said the need to fund so much overtime – worth on average nearly £3,500 a year to each member of the force in 2006-07 – was proof of the increasing pressures the police face.

He has previously described the county's police force as "scandalously shortchanged" and has called for more Government cash to raise the numbers of officers to cope with growing demands.

Mr Jackson said: "This overtime is not just down to organic growth of the population, but also to increased immigration, which has put more
pressure on policing.

"The police have also had to deal with the numbers of criminal justice bills the Government has introduced since 1997.

"We can't expect them to do all that with about the same number of police without having a big bill for overtime.

"We are asking officers to do more work, but we need funding for more
officers as soon as possible."

The figures on police overtime show Cambridgeshire spent £2.008 million on overtime in 1997-98 and £4.976 million in 2006-07.

Dividing those totals by the numbers of officers in the force in those years reveals average annual overtime earnings per officer increased from £1,542 to £3,480 over the same period.

That meant in 2006-07, officers in the county trousered the third
highest overtime bonuses in England and Wales, topped only by the Metropolitan Police and neighbouring Bedfordshire.

Their best-paying year, however, was 2005-06, when average overtime earnings were £3,959, as spending on additional hours peaked at £5.55 million.

However, a Cambridgeshire police spokesman said the increase can be attributed to "a number of factors, such as inflation and the increased demands on services".

Cambridgeshire Chief Constable Julie Spence has led calls for more funding for the force, saying it has been stretched by immigration from eastern Europe.

And it has had to cope with the strain while having one of the lowest ratios of officers to people in the country.

In fact, in 2007 Cambridgeshire had just 187 boys and girls in blue per 100,000 people. Only Lincolnshire and Surrey had fewer.

Mr Jackson said: "Good luck to the police – the work is there and they are doing it.

"But they shouldn't have to do overtime. There should be sufficient officers so they can provide an adequate service by doing their contracted hours."