New research from Go.Compare car insurance has found that 29% of UK motorists have accidentally used the wrong type of fuel when filling up their vehicle, risking significant damage and repair costs often not covered by standard insurance policies.

In a survey of more than 1,000 drivers, the comparison site found that misfuelling — such as putting petrol in a diesel engine or vice versa — is a widespread issue. Men (33%) were more likely to have misfuelled than women (23%), and younger drivers were the most at risk, with over half (54%) of those aged 18–24 admitting to making the error. In contrast, just 12% of drivers aged 55 and over said the same.

London topped the regional breakdown, with 48% of motorists in the capital saying they had filled up with the wrong fuel.

Tom Banks, car insurance spokesperson at Go.Compare, said: “Our research shows that misfuelling is a surprisingly common mistake that people make – and with many car insurance policies not covering this as standard, it could be a really costly error.

“If your policy does cover misfuelling, this could help pay for the cost of draining and flushing your tank. Some policies may also cover the cost of repairs needed because of misfuelling, but it’s important to check, as many car insurance policies might exclude misfuelling altogether, leaving you unprotected.

“In the event you do accidentally fill up with the wrong fuel, it’s important not to turn your key in the ignition or try to drive away as this can potentially cause thousands of pounds worth of damage. Provided you haven’t started the engine, you may be able to fix the problem by draining and cleaning the tank.”

Go.Compare found that 62% of car insurance policies do not offer cover for misfuelling as standard, leaving drivers exposed to unexpected repair costs. The company recommends checking both insurance and breakdown policies to understand what’s included, particularly given the frequency of such incidents.