Car Insurance Modifications List: What Affects Insurance & What Doesn’t?
23 January 2025 | 
Chris Penfold
Flashy car modifications—reminiscent of the Pimp My Ride era—might seem cool (or not, depending on your taste), but they can come with implications. From higher insurance premiums to legal penalties, it’s essential to understand the impact of modifications on your insurance before altering your car.
Every modification must be declared to your insurance provider, whether it’s cosmetic, performance-related, or safety-enhancing. Failing to do so could invalidate your insurance, leaving you unprotected in the event a claim occurs. This applies whether you have an annual policy, temporary car insurance, temporary learner insurance, or any other insurance in place. Let’s dive into what you need to know about car modifications and insurance.
What Are Car Modifications?
Car modifications are changes made to a vehicle that alter it from its original manufacturer’s specification. These include:
- Cosmetic modifications: E.g. Paint jobs or decals.
- Performance modifications: E.g. Engine upgrades or suspension changes.
- Safety modifications: E.g. Adding parking sensors.
Repairs or part replacements that restore the vehicle to its original condition do not count as modifications. Beyond this, any alteration you make to your car is classed as a car modification, and could affect your insurance…
Do You Have to Declare Modifications to Your Insurance?
Yes, every car modification must be declared to your car insurance provider. Even changes that seem minor—such as those that don’t affect how the car drives or improve safety and vehicle control—still need to be reported.
From an insurer’s perspective, any modification could increase your vehicle’s value, making it more attractive to thieves or more expensive to repair, which they must consider when calculating your premiums. This is particularly important given that vehicle theft in the UK remains at record-high levels, according to the Office for National Statistics.
Additionally, insurers may view modifications as a greater risk because they can’t guarantee:
- The quality of the parts used.
- Whether the modifications were installed correctly.
- How the changes might affect the car’s overall performance.
Declaring all modifications ensures you remain covered and avoids the risk of invalidating your policy.
List of Car Modifications That Must Be Declared
If you make any modifications to your vehicle, no matter how small, you must declare them to your insurer. While the following list includes some of the most common modifications that must legally be reported, it is not exhaustive—any modifications need to be declared as they could impact your insurance premiums:
- Engine modifications: Any upgrades or changes to the engine.
- Mechanical modifications: Adjustments to the exhaust, brakes, transmission, etc.
- Wheel modifications: Includes upgrades like alloy wheels but excludes winter wheels.
- Bodywork modifications:
- Wing and spoiler changes.
- Wheel arch alterations.
- Side skirt additions.
- Changes to exterior lights.
- Window tinting.
- Suspension modifications: Any changes that alter ride height or handling.
- Brake modifications: Upgrades or alterations to the braking system.
- Paint jobs, stickers, and decals: Custom paintwork or designs.
- Interior modifications:
- Seat upgrades or changes.
- Interior light changes.
- Pedal modifications.
- Steering wheel replacements.
Each of these changes must be reported to your insurer to avoid the risk of policy invalidation. Additionally, any modifications not listed here should also be declared to ensure your policy remains valid.
Car Modifications That Don’t Affect Insurance
While you’re legally required to declare every car modification to your insurer, some modifications are less likely to impact your premiums. In some cases, they may even reduce your costs, though this is at the insurer’s discretion. It’s always worth informing your insurer about any updates to your vehicle.
These are car mods that typically don’t affect insurance, but could actually lower your premiums in some cases – so let your insurer know about them to avoid missing out on potentially lower prices:
The Best Car Modifications That Could Lower Your Insurance Costs
- Engine Downsizing
Replacing your current engine with a smaller, lighter one can increase energy efficiency and make your car safer to drive, often resulting in lower premiums. - High-Performance Brakes
Upgraded brakes deliver better stopping power, enhancing safety and potentially reducing premiums. However, if the new brakes significantly increase the car’s value, your premiums may not decrease. - Suspension Upgrades
If your car already has multiple modifications, upgrading the suspension to improve drivability could lead to reduced premiums. - Sway Bars
Installing a sway bar enhances stability during tight turns and reduces the risk of rolling, which may lower your insurance costs. - Water Cooling System
Adding a water cooling system to boost brake performance—particularly on a heavily modified car—can help decrease premiums.
- Tow Bars
Since tow bars encourage slower, safer driving, they can lead to lower premiums. - Dash cams: If footage proves you weren’t at fault in an accident, the other driver’s insurer will cover the claim, keeping your insurer satisfied.
- Parking sensors: These safety features help you manoeuvre in tight spaces, reducing the likelihood of accidents and claims.
- Advanced Driver Assistance Systems (ADAS): Features like pedestrian detection, blind spot monitoring, and emergency braking can improve safety. Always check with your insurer before installing, as costs and benefits vary.
- Steering wheel locks: These anti-theft tools deter thieves, reducing the risk of a claim for theft.
- Catalytic converter cages: With thefts on the rise, these cages provide added security, lowering the risk of theft-related claims.
- Alarms and immobilisers: Immobilisers prevent cars from starting without the correct key, deterring theft. Many new cars already include these features, but older systems can be upgraded.
- Tracking devices: These help recover stolen vehicles, reducing the chance your insurer will need to cover a replacement.
While these modifications don’t always impact insurance premiums, some insurers might offer lower quotes if they’re included. Beyond potential savings, these enhancements can also improve safety and provide added peace of mind. However, it’s essential to check with your insurer to understand how these changes might affect your policy before committing to any modifications.
What Car Modifications Affect Insurance?
A wide range of car modifications can impact your insurance costs, by increasing your premiums. Below, we’ve outlined the modifications most likely to raise your insurance:
Car Modifications List: Mods That Could Raise Your Insurance Costs
Certain car modifications are likely to increase your insurance premiums, as insurers typically prefer vehicles to remain as close to the factory standard as possible. Below are examples of modifications that could raise your costs:
- Paintwork Changes, Stickers, and Decals
Custom paint jobs and decals can increase your car’s value, making it more attractive to thieves. Insurers may also associate certain colours and designs with higher-risk drivers. Also, be aware you might be turning your car into an ick, if you opt for neon hues. - Engine Modifications and Upgrades
Adding a turbo or tuning your engine can enhance performance but often leads to higher premiums due to increased repair costs and accident risks. Failure to declare these changes could invalidate your policy. - Cold Air Intake Changes
Even minor changes to improve engine combustion must be declared, though they may only slightly increase premiums. - Wheel Modifications
Switching to alloy wheels or painting standard ones can make your car more desirable to thieves. Some modifications, like stretched tyres or mixed tyre types, are illegal in the UK and may invalidate your insurance. - Car Light Modifications
While certain light upgrades may not impact your premiums, illegal modifications—such as coloured LED headlights or flashing under-car lights—will void your insurance. Additionally, some modifications, like adding LED strips, could increase your premiums, as they are often associated with higher-risk or irresponsible driving behaviour.
- Nitrous Oxide Systems
Legal but costly, these systems significantly increase premiums due to safety risks and higher repair costs. Additionally, if you fail to tell your insurer about these mods, they could be considered illegal, voiding your policy altogether. - Lowering Suspension
Adjusting suspension must be declared as it can make your car more prone to damage, especially on uneven roads or speed bumps. - Exhaust System Modifications
Enhancements to exhaust systems that increase engine performance will likely raise premiums. Removing silencers to create a loud exhaust is illegal in the UK. - Upgrading Brake Discs
High-performance brake discs improve safety but can increase premiums if they significantly raise your car’s value. - Bodywork Modifications
Additions like larger bumpers, side skirts, or spoilers increase accident risks and repair costs, impacting premiums. - Gear and Transmission Modifications
Changes to your gearbox must be declared, as they alter your car’s driving dynamics, which insurers consider risky. - Seat Modifications
Reupholstering or upgrading seats can increase your car’s value and premiums. If your new seats are non-compliant with safety standards this may also lead to higher costs.
Remember: Always declare modifications to your insurer, regardless of size or type, to avoid invalidating your policy. Insurers evaluate modifications on a case-by-case basis, so transparency is key.
What Car Modifications are Illegal in the UK?
While many car modifications are acceptable as long as they’re reported to your insurance provider, some are outright illegal. If you’re caught driving a car with illegal modifications—even unknowingly—you’ll automatically invalidate your insurance policy and could face serious consequences.
Below are some common illegal modifications that render a car unfit for UK roads:
- Tinted Windows Blocking Over 70% of Light
Heavily tinted windows reduce visibility, especially at night, making it harder to spot pedestrians, vehicles, and road signs. This significantly increases the risk of accidents and is therefore prohibited. - Certain Light Modifications
Flashing LED lights, blue and green headlights, heavily tinted lights, non-standard headlights, interior LED lighting, and undercar neon lights are all illegal. These modifications can dazzle other drivers and heighten accident risks. - Excessive Noise Levels
Car modifications that cause your vehicle to exceed the legal noise limit of 74dB (or 72dB for new cars, dropping to 68dB from 2026) are prohibited. Removing the exhaust silencer, for instance, can lead to disturbances and contribute to noise pollution, especially in residential areas. - Unsafe Wheel Modifications
Stretched tyres, oversized wheels, and excessively lowered suspension can compromise a car’s handling and stability, making it more dangerous to drive and increasing the likelihood of accidents. - Certain Mechanical Modifications
Removing catalytic converters, engine tuning, or injecting nitrous oxide into the combustion chamber can significantly boost a car’s power. However, these changes also make vehicles less safe to drive and more hazardous for road users and pedestrians.
So if any of the above are on your car modification wishlist, strike them off if you want to be able actually to drive your vehicle.
What Happens If You Don’t Declare Modifications on Insurance?
Failing to declare all car modifications to your insurance provider can have serious consequences:
- Policy Voidance: If your insurer discovers undeclared modifications, your policy could be voided. This means you’d be driving uninsured, which is illegal and carries significant penalties.
- Claim Denials: Any claims made on an invalid policy will be denied, leaving you to cover all repair and liability costs out of pocket.
- Higher Future Premiums: Drivers with voided policies are flagged in a national database, making it harder and more expensive to secure car insurance in the future.
- MOT Issues: Modifications are often checked during an MOT test, and some can lead to a failure. This means you won’t be able to legally drive your car until the issues are rectified.
Trying to hide modifications is not worth the risk. Always inform your insurer of any changes to your vehicle, no matter how minor they seem. It’s better to pay a slightly higher premium than face the costly repercussions of an invalid policy.
Hopefully, you are now a lot more clued up on modifications and how they affect insurance. Always remember to notify your insurer of any modifications made otherwise you risk invalidating your insurance altogether. Remember to weigh up the impact of any modifications on your insurance before you commit…
And if you’d prefer to borrow someone else’s car in a fancy colour rather than painting your own and potentially increasing your insurance premiums, our temporary car insurance provides a flexible and cost-effective solution.
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