Introduction
Modifications range from an obvious performance exhaust to alloy wheels that barely register as a change at all, yet insurers draw the line in the same place: anything different from the manufacturer's original specification. Knowing exactly where that line sits protects both your cover and your ability to claim.
This guide sets out what genuinely counts as a modification, how declaring it affects your premium, and where to find suitable cover for a more heavily modified vehicle. It complements our guides on classic car insurance and car insurance write-off categories.
Key Terms Explained
- Modification
- Any change to a vehicle from its original manufacturer specification, whether performance-related or purely cosmetic.
- Non-Disclosure
- Failing to inform your insurer of a material fact, such as an undeclared modification, which can affect a claim's validity.
- Material Fact
- Information an insurer would reasonably need to accurately assess risk, including modifications regardless of their perceived significance.
- Specialist Modified Car Insurer
- An insurer focused on modified and performance vehicles, often better placed to price and cover heavily modified cars.
- Factory Specification
- The vehicle's configuration as originally built and sold by the manufacturer, the baseline against which modifications are assessed.
- Remap
- A software change to a vehicle's engine control unit altering performance characteristics, a commonly under-declared modification.
What Counts as a Modification?
A modification is any change to your vehicle from the manufacturer's original specification. This includes obvious performance changes, but also many changes that owners don't always think to declare.
- Engine tuning or remapping
- Exhaust system changes
- Suspension or brake upgrades
- Alloy wheels not fitted as standard
- Body kits, spoilers or styling changes
- Window tinting beyond factory specification
- Upgraded audio or in-car technology systems
Why Modifications Matter to Insurers
Modifications can affect a vehicle's performance, value, and attractiveness to thieves, all of which influence risk. Performance modifications may increase the likelihood or severity of an accident, while high-value cosmetic changes can increase the cost of a claim, and some modifications increase the risk of theft. Certain popular and higher-value models are also specifically targeted through keyless relay attacks, a distinct theft method covered in our Keyless Car Theft and Relay Attack Insurance UK guide.
| Modification Type | Typical Insurer Concern |
|---|---|
| Engine remap/exhaust | Increased performance, accident risk |
| Alloy wheels/styling kits | Increased repair or replacement cost |
| Audio/technology upgrades | Increased theft appeal |
Common Situations
Modifications Made Before You Owned the Car
Any modification present on the vehicle, regardless of when or by whom it was made, should generally be declared to your insurer. Buying a car with existing modifications doesn't exempt you from the declaration requirement, since the risk profile is the same regardless of who fitted the change.
Reverting Modifications
Removing a modification and returning a car closer to standard specification should also generally be declared, since this can affect its risk profile, sometimes reducing your premium, and keeps your insurer's records accurate.
Manufacturer-Approved Performance Packs
Whether a performance pack counts as a modification depends on whether it was factory-fitted as part of the original specification or added afterwards as a dealer or aftermarket option, so check with your insurer if you're unsure which category applies.
Private Registration Plates
A personalised number plate doesn't affect the vehicle's specification or risk profile and generally doesn't need declaring as a modification, distinguishing it clearly from genuine mechanical or cosmetic changes.
How Modifications Affect Your Premium
Performance Modifications
Engine, exhaust and suspension changes that increase power or alter handling are typically viewed as higher risk and can noticeably increase premiums.
Cosmetic Modifications
Purely cosmetic changes, such as styling kits or upgraded wheels, may have a smaller impact but can still affect premiums, particularly if they increase the vehicle's value or theft appeal.
Declaring Modifications Correctly
- List every change from factory specification. Include cosmetic as well as performance changes.
- Contact your insurer as each change is made. Don't wait until renewal to declare.
- Confirm pre-existing modifications on a purchased vehicle. Declare these at the point of taking out cover.
- Update your insurer if you revert a modification. This can also affect your premium.
- Keep records of declared modifications. Useful evidence if a dispute ever arises.
Finding Insurance for Modified Cars
Standard insurers may still cover lightly modified vehicles, but for more heavily modified cars, specialist modified car insurers may offer more suitable and competitively priced cover, as they have more experience assessing this type of risk. Some mainstream insurers decline heavily modified vehicles entirely, making specialist providers particularly valuable for enthusiasts with substantial performance or styling changes.
Common Mistakes to Avoid
- Assuming minor cosmetic changes don't need declaring
- Not declaring modifications present when you bought the car
- Waiting until renewal to declare a recent modification
- Forgetting to update your insurer after removing a modification
- Assuming a decline from one insurer means no cover is available anywhere
- Not keeping records of declared changes over time
Frequently Asked Questions About Car Insurance Modifications
Do I need to declare alloy wheels as a modification?
If they are not part of the original manufacturer specification, yes, they should generally be declared even though the impact on your premium may be small.
Will modifying my car always increase my premium?
Not always, but many modifications, particularly performance-related ones, tend to increase perceived risk and therefore premiums.
What happens if I don't declare a modification?
This can lead to a claim being reduced or rejected, or the policy being treated as void from the date of the undeclared change.
Can I get insurance for a heavily modified car?
Yes, specialist modified car insurers often provide more suitable cover and pricing for heavily modified vehicles than mainstream insurers.
Do I need to declare modifications made before I bought the car?
Yes. Any modification present on the vehicle, regardless of when or by whom it was made, should generally be declared to your insurer.
Does removing a modification need to be declared too?
Generally yes, since reverting a car closer to standard specification can also affect its risk profile and should be updated with your insurer.
Are manufacturer-approved performance packs treated as modifications?
This depends on whether the pack was factory-fitted as part of the original specification or added afterwards, so check with your insurer if you're unsure.
Does declaring a modification always mean a higher premium?
Not necessarily, some modifications have minimal pricing impact, though declaring accurately matters more than the size of any premium change.
Can insurers refuse cover because of a modification?
Yes, some insurers decline heavily modified vehicles entirely, which is one reason specialist modified car insurers exist to fill that gap.
Does a personalised number plate count as a modification?
No, a private registration plate doesn't affect the vehicle's specification or risk profile and generally doesn't need declaring as a modification.
Conclusion
Whether cosmetic or performance-related, modifications should always be declared to your insurer to keep your cover valid, including changes present before you owned the car and any you later reverse. While some modifications increase premiums, comparing specialist modified car insurers can help you find suitable cover that reflects your vehicle accurately.