Research has found that even tiny modifications to your car could both void the insurance and drive up premiums.

Motoring publication Auto Express teamed up with the British Insurance Brokers’ Association (BIBA) to work out some of the unusual modifications that could be costly when it comes to insurance.

Failing to declare tiny modifications – including displaying allegiances to sports teams or if your car wears paint protection – poses the risk of invalidating your insurance, as some insurers are very strict about what’s classed as a ‘modification’. Some firms require absolutely no deviation from the ‘standard’ specification of the car.

Even factory-fitted options, if not declared, could drive up premiums, if they increase the attractiveness of the car to thieves.

But the research also uncovered just how much certain modifications can drive up insurance premiums. Even small changes like an aftermarket satellite navigation could add an additional 11 per cent onto your premiums, along with increased performance badging (8 per cent) and decals (16 per cent).

But two performance-based changes – a NOS kit and an additional turbocharger could increase your insurance by a massive 178 per cent over the standard car, according to Auto Express.

Hugo Griffiths, consumer editor at Auto Express, said: “Many motorists will be surprised by the strict definition of modification, and how even a sticker in the back window could void your policy.

“Failing to declare something as humble as paint protection film or different alloy wheels could void a policy entirely, potentially costing thousands in the event of an incident, and even putting motorists at risk of a £300 fine and 6 penalty points.

“And, in the case of potentially controversial messages on stickers, it’s best to keep your opinions to yourself, or be prepared to share them with your insurer.”