Car Modifications and Insurance in the UK: What You Must Declare

Modifying a car is hugely popular in the UK, from simple alloy wheel upgrades to full engine remaps and body kits. But every modification you make — or buy a car with — has insurance implications. Fail to declare a modification and your insurer can void your entire policy, reject your claim, and leave you personally liable for all costs.

This guide explains what counts as a modification, which ones affect your premium, how to declare them properly, and what to do if you are buying a car that has already been modified.

1. What Counts as a Modification?

In insurance terms, a modification is anything that has been changed from the manufacturer's original factory specification for that specific variant. This includes:

• Aftermarket alloy wheels — Different size, style, or brand from the factory option
• Exhaust systems — Sports exhausts, decat pipes, backbox replacements
• ECU remaps — Software changes to increase engine power or torque
• Window tints — Any tinting beyond factory-fitted glass
• Lowered suspension — Coilovers, lowering springs, air suspension
• Body kits — Front splitters, side skirts, rear spoilers, wide arches
• Turbo or supercharger — Forced induction additions or upgrades
• Dash cams — Technically a modification, though rarely affects premiums
• Sound systems — Aftermarket speakers, amplifiers, subwoofers
• Roof racks and roof boxes — Non-factory additions

2. Modifications That Increase Premiums

Performance modifications have the biggest impact on insurance costs because they increase the car's speed, power, or desirability to thieves:

3. Modifications That Usually Don't Affect Premiums

Some modifications are considered neutral or even beneficial by insurers:

• Parking sensors — Reduce the risk of low-speed bumps
• Hands-free phone kit — Safer than holding your phone
• Dash cam — Some insurers offer discounts for dash cam users
• Thatcham-approved alarm or immobiliser — May actually reduce premiums
• Roof rack — Minimal impact unless it is a permanent fixture
• Tow bar — Typically no increase (but declare it)

4. How to Declare Modifications

1. Call your insurer — Most modifications cannot be added online and need a phone call
2. Describe the modification accurately — Provide brand, type, and what it changes about the car
3. Get written confirmation — Ask for an email or letter confirming the modification is on your policy
4. Check the premium change — Your insurer will tell you if the premium increases and by how much
5. Declare at renewal too — When switching insurers, list every modification from scratch

5. What Happens If You Don't Declare

Failing to declare modifications is treated as misrepresentation or fraud. The consequences are severe:

• Policy voided — The insurer can cancel your policy as though it never existed
• Claim rejected — If you have an accident, the insurer can refuse to pay any claim
• Personal liability — You become personally responsible for all damage costs, including third-party injuries
• Fraud record — The insurer may report you to the Insurance Fraud Bureau (IFB), making it difficult and expensive to get insurance in future
• Criminal prosecution — In serious cases, undeclared modifications can lead to fraud charges

6. Specialist Modified Car Insurers

If your car is heavily modified, mainstream insurers may refuse cover or charge prohibitively high premiums. A number of UK insurers and brokers specialise in modified, performance, imported and classic cars, and will often price them more sensibly than a mainstream insurer.

Rather than starting from a brand name, compare specialists on what actually matters at claim time:

• Agreed value — will they agree your car's value in writing, including modifications, before you buy?
• Declared modifications — do they accept your full list, in writing, without loading the premium later?
• Parts and repairs — will they use specialist or original parts, or insist on standard equivalents?
• Track and show use — is it covered, excluded, or an add-on?

Agreed value is the one worth pushing on: an agreed-value policy pays out the actual value of your modified car, modifications included, rather than the standard book value of an unmodified version.

SortedCars does not recommend or arrange insurance, and we receive no commission from any insurer.

7. The V5C and Modifications

Your V5C (logbook) records key details about your car. Certain modifications must be notified to the DVLA as well as your insurer:

• Engine swap — If you change the engine to a different size or type, this must be reported to the DVLA and updated on the V5C
• Colour change — A full respray or wrap in a different colour must be reported
• Structural changes — Major body modifications that change the car's structure

Cosmetic modifications (alloys, body kits, exhausts) do not usually need to be reported to the DVLA — gov.uk lists the changes that must go on the V5C — but they absolutely must be declared to your insurer.

8. Selling a Modified Car: Buyer's Insurance Implications

If you are selling a modified car, the buyer needs to know about every modification so they can declare them on their insurance. If you are buying a modified car:

• Ask for a full list of modifications before purchasing
• Get insurance quotes with the modifications declared before committing to buy
• Check the V5C for engine changes or other DVLA-notifiable modifications
• Consider whether modifications are reversible if you want to bring insurance costs down

Final Thoughts

Modifying your car is perfectly legal, but you have a duty to declare every change to your insurer. The consequences of not doing so — voided policy, rejected claims, personal liability — far outweigh any premium saving. If your modifications push mainstream premiums too high, use a specialist insurer who understands modified cars and will properly cover your investment.

This guide provides general information and is not legal or insurance advice. Always check with your insurer about specific modifications and their impact on your policy. SortedCars is not a lender, credit broker, insurer or financial adviser. We receive no commission from any provider mentioned in this article.