Lancashire Police spent more than £2m on unmarked police cars over the past three years - the second highest amount in the country.
The bill included cash spent on expensive high performance cars for senior officers including Audis, BMWs and a Mercedes.
The figures were released under the Freedom of Information Act and show the force spent the second highest amount in England, behind West Midlands Police.
Data revealed more than £600,000 was spent on 76 Vauxhall Corsas between April 2010 and March 2013, more than £85,000 on eight Vauxhall Astras and more than £45,000 on Vauxhall Insignias.
There were also purchases of cars costing more than £30,000 including, a BMW X5, Audi A6, Audi A5, Audi A4 and a Mercedes E Class.
A spokesman for the force said: “Lancashire Constabulary operates a fleet of nearly 1,000 vehicles and a large percentage of these vehicles are unmarked but are used for operational policing.
“The vehicles also include pool cars, and chief officer cars, in addition to those used for covert enforcement and surveillance. Many vehicles are plain vans and the majority of these vehicles are low performance and used on a daily basis.”
Jonathan Isaby, chief executive of pressure group the TaxPayers’ Alliance, added: “The police budget should be spent fighting crime, not performance cars for ferrying police chiefs around.
“Forces need vehicles for undercover work but that’s not a reason to buy them for those spending their life behind a desk. Axing flash run-arounds for police chiefs is a simple way to save taxpayers’ money.”