Careless police officers have wasted more than £8,000 of taxpayers' money in the past three years by filling up their force cars with the wrong type of fuel.

In total, police cars owned by Hertfordshire Constabulary have been misfuelled on 57 separate instances during the 36-month period. 

Figures released under the Freedom of Information Act revealed that on those occasions, diesel cars were wrongly filled with petrol.

The cost of the errors at the pump since 2012 amounts to at least £8,211, which does not include refilling the fuel tank with the correct fuel after repair.

The models of the cars misfuelled included a Vauxhall Corsa, Astra, Zafira and Insignia, a Volvo V70 and S80 and a VW Golf and Passat. 

Andy Silvester said on behalf of The TaxPayers' Alliance: "Even the Keystone Cops didn't confuse petrol and diesel. Not only does this bungling cost the taxpayer a pretty penny, it takes a police car off the road. This kind of waste must be cut out."

Olivia Finucane, on behalf of Hertfordshire Constabulary, said: "Whilst we wish these incidents would not occur, we must remember that police officers work in a high-pressure environment and, occasionally, mistakes do occur when fuelling vehicles.

"Hertfordshire Constabulary are always looking at ways to make savings and we been nationally identified as one of the most financially shrewd forces in the country.

"We have had fifty seven incidents of misfuelling over the last three years - with six occurring in this financial year ( April 2014 - October 2014). The decrease in such indents this year highlights work we have taken to address and rectify this issue including extra signage on the fuel caps on all of our marked fleet."

Hertfordshire Constabulary has a fleet of six hundred and fifty vehicles which have travelled a total of 11.75 million miles over the last three years. 

Although pumping diesel into a petrol engine causes little damage, filling up a diesel engine with petrol can cost £5,000 per car to repair. The cost is especially high if officers ignore their mistakes and drive off, circulating the incorrect fuel within the engine.

According to the AA, at least 150,000 drivers fill up their cars with the wrong fuel every year.