When you want to turn your car into something which truly reflects your style and personality, it’s sure to attract someone’s attention - and that’s your insurance company.

You’ve probably seen that any application you make for car insurance asks you whether your car has been modified in any way from the standard specification.

That’s because, while a car remains in the same state as when it left the factory, it’s easier - and cheaper - to repair, because not just main dealers, but also lots of other suitably qualified experts, can do the work.

But as soon as you start adding extra bits and bobs - whether it’s in an effort to boost the car’s performance or intended purely for cosmetic reasons - your insurance company is likely to start to get nervous.

Comparison website Moneysupermarket.com analysed 2.3 million insurance quotes provided for modified vehicles, and found that, in the most extreme cases, insurance premiums doubled once a substantial modification was notified to an insurer.

It defines a modification as anything intended to alter the aesthetics, function or performance of a car, and which means it no longer meets the original factory specification.

And the research found that insurers were least keen on the following modifications, resulting in jumps in average premiums as shown in brackets:

• Turbocharging the engine (132%)
• Modifying the bodywork, e.g. by fitting a body kit (66%)
• Tweaking the transmission (63%)
• Fitting a complete body kit with extra panels (57%)
• Removing seats, adding a roll bar or roll cage (41%)
• Getting a custom paint job (36%)
• Uprating the brakes (36%)
• Altering the exhaust system (26%)
• Tweaking the suspension (25%)
• Adding stripes, badges or other decals (22%)

So, if you’ve added any of these features to you car, you should expect to have to pay more for your insurance.

But you shouldn’t be tempted to just not tell your insurance company about any tweaks - any modification could be considered an alteration to your car’s original specification, so should be notified to your insurer. If you keep schtum, and any changes become apparent during inspections as part of a claim, that’s when you could really land yourself in trouble, with your insurer refusing to pay up for the repair, and even cancelling your policy.

Kevin Pratt, consumer affairs specialist at Moneysupermarket, said: “For some, modifications are an addictive hobby, but the most important thing to remember is to inform your insurer of any changes, preferably before you make them, so you can find out the impact on your insurance. You certainly shouldn’t wait until it’s time to renew your policy.”

But Some Mods Actually Save You Money…

These are usually the ones which are likely to mean you having to drive more carefully or which could force you to drive more slowly.

The ones which could cut your premium include:

• parking sensors (estimated to cut premiums by 13%)
• having a tow bar fitted - provided it’s done professionally - could bring a 20% reduction - and
• letting your insurer provide you with a ‘black box’ to help monitor your driving behaviour

The research found that female drivers are on average 40 per cent more likely to have opted for parking sensors on their car - although it did steer clear of making any judgment on whether this was proof that they were worse at parking than men!

We want to know about your experiences of trying to get cover for your car if you’ve had it modified in any way. Please contact us via Twitter @motorrange.