Police officers have pocketed £3.8 billion in overtime over the past 10 years, a study found today.
More than a quarter of this, £1 billion, was spent by the Metropolitan Police alone, with every officer picking up an average of £4,271 in overtime last year.
Home Secretary Theresa May put herself on a collision course with rank-and-file officers last week when she warned that police pay cuts were "unavoidable" amid efforts to minimise frontline job losses.
A review of police pay and conditions by the former rail regulator Tom Winsor tomorrow is expected to recommend slashing at least £180 million off annual bonuses by scrapping special priority payments handed out to selected officers at Christmas and competency threshold payments.
Three-quarters of the annual police budget, £11 billion, goes on pay, and Mrs May told forces that must change.
But the Police Federation warned any cuts on top of the two-year public sector pay freeze would damage morale, adding that she "clearly undervalued" officers' work.
The annual overtime bills peaked in 2007/08 when forces in England and Wales clocked up more than £437 million, the analysis by the Policy Exchange showed.
From an annual overtime bill of £208 million in 1998/99, the total across the 43 forces more than doubled to £437 million in 2007/08, falling slightly to £382 million last year.
Police numbers rose by just 12%, excluding an additional 17,000 PCSOs, over the same period, the think-tank said.
One in three forces have managed to cut their overtime bills in the past five years compared with 2000-2005, but the average spent on each officer by two-thirds of forces has increased.
Surrey, Wiltshire, Lincolnshire, and Cumbria all reduced the amount they spent on overtime over the past 10 years, with Surrey's average bill per officer falling by £864, more than a quarter.
But spending on overtime in Warwickshire was still out of control, the report said, with the average bill per officer increasing by more than half (£1,036) over the same period.
Set a target for a 15% reduction in police overtime between 2002 and March 2006, only eight forces achieved any savings at all and the City of London Police was the only force to exceed it.
"It is a damning indictment of police management and the effectiveness of the target-setting process that during this period the total overtime bill for forces increased by 29%," the report said.
The figures, from the Chartered Institute of Public Finance and Accountancy, also showed Sussex Police cut their £14 million in 2000/01 by almost half in 12 months, now keeping the annual bill at around £6 million.
"The success of Sussex in reducing and keeping control of police overtime has been attributed to embedding of overtime management into the organisation," the report said.
This included ensuring supervisors were aware of the need to manage overtime and the development of a web-based overtime management tool.
The report added that there was "some anecdotal evidence that inappropriate use of overtime may be due to the culture in the police service and staff expectation, in addition to poor management and planning".
Blair Gibbs, head of crime and justice at the Policy Exchange, said: "Paying police officers overtime can makes sense in some cases, but police forces have allowed these payments to spiral out of control, with a huge amount spent over the last decade even while officer numbers have increased.
"The majority of forces have not gripped the overtime problem and as a result some officers have earned thousands in additional salary because of bad planning and management.
"Overtime payments need to be reformed so the costs to the taxpayer can be brought down. Police officers should only be paid for overtime when it is absolutely necessary and appropriate."