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

In total, police cars owned by Hertfordshire Constabulary, which includes Borehamwood and Potters Bar, have been misfuelled on 57 separate occasions 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 amounts to at least £8,211 since 2012, and does not include refilling the fuel tank with the correct fuel after repair.

Cars misfuelled include Vauxhalls, a Volvo and a VW Golf.

Although pumping diesel into a petrol engine causes little damage, fuelling a diesel engine with petrol can cost £5,000 per vehicle 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.

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 have 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 (from April 2014). The decrease in such incidents 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."