Spending on police overtime has nearly doubled over the past decade despite record numbers of police officers, a report said today.
Overtime payments in England and Wales soared by around 90% between 1999 and 2009, hitting £400 million last year, according to the Centre for Crime and Justice Studies (CCJS).
The rise came as the number of police officers reached an all-time high of 142,151 in 2009 - 15,337 higher than a decade ago, the study found.
Researchers said overall policing costs also grew by a "remarkable" 48% over the 10-year period, from £9.8 billion to £14.5 billion.
After the future of the policing budget became one of the key battlegrounds during the general election campaign, the CCJS said its findings meant that a public debate about police priorities was needed "more than ever".
The centre's director Richard Garside questioned the value obtained from the massive spending hike as well as the rationale for the jump.
He said: "Spending has gone up by nearly a half but the value of this huge increase is much harder to pin down.
"We now have the largest police service ever. Yet there seems to be no clear rationale behind this incremental growth, nor a clear measure of its success.
"Is there a point in having a 'reserve army' of this magnitude? Now more than ever we need a public debate about priorities and choices."
The report's compilers said the rise in overtime appeared "counter-intuitive" given the current size of the workforce.
But "the Home Office recognises its (overtime's) necessary part in responding to unexpected major incidents", they added.
Spending on staff made up just over three-quarters of the overall costs (76%), with the rest coming through capital expenditure, property, transport and other services.
The report also said the spending increase has been sustained by "significant increases" in council tax bills.
It calculated that from 2003/04 onwards, council tax had provided around a fifth of police revenue expenditure.
The growth in civilian staff, including police community support offices, has also outstripped that in police officers, the report said.
There were 77,609 civilian staff last year, up from 52,975 a decade ago. The number of PCSOs also reached 16,331 in 2009, since they were introduced during 2002.
The report concluded: "The fact that spending has so vastly increased in the past decade should be a stimulus to fresh thinking about the shape and size of the police service as a whole.
"A new political debate about police numbers could become a sterile diversion unless there is a fundamental discussion about what the police are for, and what that means for the public purse."Reuse content