Information released by forces across the country show Surrey was one of the biggest spenders on hire cars compared to other similar-sized forces.
Police spokesman Nathan Rees defended the sum spent and said that unmarked hire cars were used on operations if a short-term need arose.
The force also said that in the past six months, hire cars had been singled out as an expense that could be reduced by making more permanent police vehicles available.
"The use of short-term hire makes financial sense for short periods," the spokesman said.
"The alternatives would result in spare vehicles being under used, which would lock up resources in a depreciating asset. "To hire vehicles on short-term rates over a long period would not make financial sense."
He added that Surrey Police used a regional tender process that made sure the force got the best deals possible on hire vehicles.
The force spent £418,000 on hire cars in the 2004/05 financial year – the highest sum in the past five years.
In total, the force has 418 unmarked police cars and 331 marked cars.
Matthew Elliot, chief executive of the Taxpayers' Alliance, said: "Everybody knows that it is more expensive in the long run to rent something so the police should economise and spend our money more wisely."
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