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Before you make changes to your car, it's important to understand how modifications can affect your insurance costs. The short answer is: yes, most modifications will increase your premium – but not always.
Car modifications must be declared to your insurer in the UK, regardless of whether they are performance or cosmetic changes. Failing to disclose modifications can invalidate your policy entirely, meaning your insurer could refuse to pay out on claims.
Before you make changes to your car, it's essential to understand how modifications can affect your insurance costs. The short answer is: yes, most modifications will increase your premium. But there's more nuance to it than that, and some changes can actually bring your costs down.
With the Financial Ombudsman Service reporting a rise in cases where drivers have had claims rejected due to undeclared modifications, getting this right has never been more important. Here's everything you need to know about car modifications and insurance in 2026.
In the eyes of insurers, a modification is any change made to your car that alters it from the manufacturer's original factory specification. This definition is deliberately broad and covers far more than most drivers realise.
Performance modifications:
Cosmetic modifications:
Security modifications:
Practical modifications:
Even selecting alloy wheels as an optional extra when buying a new car is technically a modification that should be declared. If you've bought a car that was previously modified by someone else, those changes still need to be disclosed on your policy.
Insurance companies assess modifications as additional risk factors. When you change your car from its factory settings, several things shift in the insurer's calculations:
Modified parts are typically more expensive to fix or replace than standard components. Custom bodywork, performance brakes, or upgraded exhausts require specialist labour and parts that aren't always readily available. With repair costs already accounting for 64% of all motor insurance claims (totalling £1.9 billion in Q3 2025 alone), insurers are particularly sensitive to anything that increases potential repair bills.
Modifications often increase your car's overall value. If your vehicle is written off or stolen, the insurer faces a larger payout to replace it. This is particularly relevant for comprehensive policies where the insurer covers the full value of the vehicle.
Modifications like engine remaps, turbochargers, or exhaust upgrades can significantly increase your car's power output. Insurers view this as heightened accident risk, particularly for younger or less experienced drivers. Even handling modifications like lowered suspension can affect how your car behaves in emergency situations.
Modified cars can be more attractive to thieves, especially those with expensive visible upgrades or eye-catching custom features. With vehicle theft in the UK reaching concerning levels (over 121,000 vehicles stolen in the year ending March 2025), insurers factor theft risk heavily into their calculations. Theft-related claims averaged £11,800 in Q3 2025.
The premium increase varies significantly depending on what you've changed. You can generally expect modified car insurance to cost anywhere between 10% and 100% more than a standard policy. For heavily modified vehicles with multiple performance upgrades, premiums can exceed even that.
Not all modifications push your premium up. Some security-focused changes can actually bring costs down, and insurers actively reward drivers who take steps to protect their vehicles.
Thatcham Research is the automotive industry's security testing body, and insurers place significant value on their certification. Installing Thatcham-approved security can lead to meaningful premium reductions:
GPS trackers (Category S5 or S7): These significantly increase the chance of recovering a stolen vehicle. Many insurers offer substantial discounts, and some require them for high-value vehicles.
Alarms and immobilisers: Most modern cars come with factory-fitted systems, but upgrading to a more advanced Thatcham-approved aftermarket system can reduce premiums.
Steering wheel locks: While the direct discount may be small, these serve as strong visual deterrents that protect your no-claims bonus.
You must tell your insurance company about any changes to your vehicle, no matter how minor they seem. The Financial Ombudsman Service has highlighted increasing numbers of cases where vehicle owners have faced significant financial losses because they unknowingly invalidated their insurance by not declaring modifications.
If you don't declare modifications and need to make a claim, your insurer could:
This applies whether you made the modifications yourself or bought a car that was already modified. In one Financial Ombudsman case, a driver had their claim rejected because the car had alloy wheels three inches larger than standard, even though the driver claimed not to know about the modification.
Because different insurers treat modifications very differently, shopping around is essential. Some mainstream insurers load premiums heavily for any modifications, while specialist providers may offer significantly better rates for the same vehicle.
When getting quotes, be completely honest and detailed about all modifications. Provide specific information about brands, specifications, and whether work was done professionally. This helps insurers give you accurate quotes and ensures you're fully covered if you need to claim.
Use the free comparison tool via Brumble to get quotes from multiple insurers, including specialists in modified vehicles.
Compare Quotes NowCar modifications and insurance in the UK require careful consideration in 2026. While most changes to your vehicle will increase your premium, the key to managing costs is transparency and comparison shopping.
Always declare every modification to your insurer, no matter how small. The financial consequences of undeclared changes, from rejected claims to voided policies, far outweigh any short-term savings on premiums.
If you're planning modifications, consider the insurance implications before you start. And if you're looking to reduce your premium, security upgrades like Thatcham-approved trackers and immobilisers can make a real difference, both to your insurance costs and to your peace of mind.
With the average UK car insurance premium at £551 (Q3 2025), shopping around with specialist modified car insurers is essential to find competitive rates. Remember that building your no-claims bonus remains one of the most effective ways to reduce premiums, whether your car is modified or not.
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