Modified Car Insurance: What Modifications Do to Your Premium (2026)

Why every modification needs to be declared

Insurers price a policy based on the risk profile of the car as described — engine power, security features, likely repair costs, and how the car is likely to be driven. A modification that increases power, changes handling, or increases the car's value or attractiveness to thieves changes that risk profile, and insurers require it to be declared so the premium reflects the actual vehicle being insured, not a theoretical standard version of it.

What typically counts as a modification

• Performance changes: engine remapping/chipping, turbo or supercharger upgrades, exhaust system changes, air intake modifications.
• Handling changes: lowered or uprated suspension, larger brakes, different wheel sizes.
• Cosmetic changes: body kits, spoilers, tinted windows, non-standard paint finishes or wraps, aftermarket alloy wheels.
• Audio/electronics: some significant aftermarket sound systems or additional electronics beyond factory-fit.

Even changes that seem purely cosmetic can affect insurance pricing, since they can increase the car's value, its attractiveness as a theft target, or the cost of parts if damaged.

The cost of not declaring

If an insurer discovers an undeclared modification when investigating a claim — even one seemingly unrelated to the modification (for example, a theft claim where the car turns out to have an undeclared remap) — the claim can be reduced, refused, or the entire policy voided, on the basis that the insurer never had accurate information to price the actual risk. This is one of the most common and costly mistakes modified-car owners make.

Mainstream vs specialist insurers

Mainstream insurers often respond to declared modifications by significantly loading the premium, or in some cases declining cover for certain higher-risk modifications altogether. Specialist modified-vehicle insurers, by contrast, build their underwriting specifically around performance and modified cars, and can sometimes offer more appropriately priced (and sometimes cheaper) cover than a mainstream insurer's blanket loading — worth getting quotes from both types before assuming the mainstream quote is the only option.

A practical checklist before insuring a modified car

• List every change from factory standard, however minor it seems.
• Get quotes from both mainstream and specialist insurers to compare.
• Keep receipts and documentation for modifications, useful both for accurate declaration and for any future claim.
• Re-declare if a modification is added or removed after the policy starts.

Sources

• gov.uk: Vehicle insurance
• Association of British Insurers: Modified vehicle insurance guidance
• FCA: Insurance disclosure requirements