The car modifications that could add hundreds to your insurance - and the illegal ones to avoid

For many drivers making their car individual is part of the fun of ownership but new research has found that aftermarket modifications can push up your insurance by hundreds of pounds.

A comparison of insurance quotes for some of the UK’s best selling cars revealed that on average modifications add 81 per cent to a premium, with some changes pushing up prices by 153 per cent.

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With the average premium currently standing at more than £800 that’s a significant increase for most drivers.

The comparison by leasing firm Rivervale Leasing looked at the 10 best-selling cars in the UK found that changes to a car’s engine, bodywork and wheels brought the biggest increase in insurance costs - an average of 153 per cent more than an unmodified car.

Since such modifications are often associated with performance upgrades, it’s not surprising that they add the most to insurance bills but interior upgrades were also found to make a significant difference - adding an average of 96 per cent to a regular policy.

Fancy paintwork or adding a wrap or stickers to a car’s shell not only costs a lot but also adds an average of 89 per cent to a policy yet suspension modifications which could affect how a car handles adds 50 per cent.

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Even the act of installing air conditioning can push up your premium by a quarter.

The research found that of the UK’s 10 best selling cars the Volkswagen Polo was most affected by aftermarket modifications. Calculated using an averaged number of modifications, it was found to be 134 per cent more expensive after modification than before. The Kia Sportage saw the second largest impact from mods, with insurance costs jumping 115 per cent.

At the opposite end of the table, modifying a Ford Kuga or Vauxhall Corsa brings increases of 36 and 37 per cent respectively.

Undeclared and illegal mods

With such sharp increases in cost it might be tempting to simply not mention them to your insurer but that could end up costing you even more.

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Failing to disclose a modification is likely to invalidate your insurance. This not only means that in the event of a claim you won’t be covered but means you will be driving illegally. If you are caught driving without insurance, the police can give you a fixed penalty notice of up to £300 and six points on your licence. If the case goes to court you could get an unlimited fine and a disqualification from driving.

Certain modifications could also see you violating road traffic rules, rendering your car illegal. For instance, a front window tinted to block more than 30 per cent of light is illegal, as is displaying any blue lights on your car or fitting a number plate with a non-regulation font, spacing or design.

Fitting an aftermarket exhaust or uprated sound system could even see you fall foul of noise regulations and left liable to a fixed penalty notice.