Police officers in Northern Ireland cost much more than their counterparts in England and Wales, figures show.
Almost half of payments to officers were linked to the security threat, an independent watchdog's review said.
Its report said: "There is little doubt that the security threat and legacy issues such as the re-investigation of historical cases from the Troubles continue to place a noteworthy demand on the resources of the PSNI."
Expenditure records for 2011/12 showed the payroll for police officers and staff in Northern Ireland accounted for £538 million, 46% of the running cost of the force. Spending on police pensions was relatively high at 24% of running costs.
Ongoing work by Her Majesty's Inspectorate of Constabulary (HMIC) on value for money has found that the PSNI workforce costs significantly more than any comparable force in England and Wales, the Inspectorate said. No concrete figures were available for English and Welsh totals as the report is still being finalised by HMIC.
"The costs per police officer are significantly more expensive than the average in England and Wales," its report added.
"The use of Police Community Support Officers (PCSOs) in England and Wales (10% of all police officers) has certainly reduced their comparative costs relative to the PSNI."
Police staff costs in the PSNI are also higher than the average for England and Wales, though the difference is much less than comparative figures for officers.
Non-staff costs are nearly three times more expensive than the average cost per head of population in England and Wales, much of which has been attributed to the extra security costs such as an armoured fleet of vehicles and Land Rovers, the report said.