Car Insurance for Modified Cars UK 2026: Declaration Rules & FCA Position

A modified car is any vehicle whose specification differs from the manufacturer's standard factory output. For motor insurance purposes, any modification - whether it improves performance, changes the appearance, enhances security or alters the structure - is a material fact under CIDRA 2012 that must be declared to the insurer. Insurers treat modifications as material because they affect the risk of accident, theft, total loss value and repair cost relative to the standard specification used when assigning the Thatcham insurance group. For the full market overview, visit the car insurance hub. For insurance group context, see our cheapest cars to insure UK 2026.

Understanding how different modification categories are treated by insurers - and the specific legal consequences of non-disclosure - allows modified-car owners to obtain appropriate cover and avoid voided policies.

The CIDRA 2012 disclosure obligation for modifications

Under the Consumer Insurance (Disclosure and Representations) Act 2012 s.2-3, a policyholder must take reasonable care to give a fair presentation of the risk. This includes answering all questions asked by the insurer honestly and completely. Where the insurer asks about modifications (as virtually all do), any modification to the standard specification is a material fact that must be declared.

Modification categories and insurer treatment

Thatcham security ratings and modifications

Thatcham Research (thatcham.org) assigns security ratings to approved security devices - not to body modifications or performance upgrades. The Thatcham security rating system for devices is:

A Thatcham S5/S6/S7 tracker is distinct from a performance or cosmetic modification. Fitting one is a modification that must be declared, but it typically reduces rather than increases the premium and may be a mandatory condition of cover for high-value vehicles. Confirm with your insurer before fitting.

MOT vs insurance distinction

A vehicle that passes its MOT is confirmed as roadworthy according to DVSA standards (gov.uk/get-your-vehicle-tested). MOT approval does not mean a modification is acceptable to insurers or vice versa. These are entirely separate frameworks:

A modification can be MOT-legal and insurance-voidable. A vehicle with a remapped ECU may pass its MOT (the MOT tests roadworthiness, not performance specification) but the insurer may decline or void cover if the modification is not declared. The two regulatory systems are operated independently by DVSA (DVSA/MOT) and the FCA (insurance).

A modification can be insurance-accepted but MOT-failing. Some cosmetic or structural changes that mainstream insurers will cover may fail the MOT if they affect lighting, visibility, noise or structural integrity. Always confirm modifications against both the DVSA MOT standards and the insurer's terms.

For the specialist modified-car market, BIBA-member brokers (biba.org.uk/find-insurance/) access specialist FCA-authorised insurers. For the full market overview, visit the car insurance hub. For the complaint route if a modification disclosure is handled unfairly, see our FOS guide.

Frequently Asked Questions

Do I need to declare alloy wheels to my insurer?

Yes, if the alloy wheels differ from the manufacturer's standard specification for your specific model and trim. Non-standard alloys are a modification because they affect repair/replacement cost and can affect theft risk. Failure to declare constitutes a qualifying misrepresentation under CIDRA 2012. Standard alloys supplied by the manufacturer as factory fit are not a modification and do not require separate declaration.

Will modifications void my insurance if I don't declare them?

A failure to declare a material modification is a qualifying misrepresentation under CIDRA 2012. Where the non-disclosure is deliberate or reckless, the insurer may void the policy from inception under Schedule 1 para.5, retain the premium, and refuse all claims. The driver is then effectively uninsured and exposed to an RTA 1988 s.143 prosecution. Even an innocent failure to declare can result in claims being reduced proportionately.

Does fitting a tracker reduce my car insurance?

Fitting a Thatcham-approved tracker (category S5, S6 or S7) may reduce the theft component of a motor insurance premium with some insurers, particularly for vehicles with an elevated theft risk profile. The device must be Thatcham-rated to qualify; the insurer's specific discount (if any) is stated in their product terms. For high-value or high-theft-risk vehicles, a tracker may be a mandatory condition of cover rather than an optional discount trigger. Confirm the position with your insurer before fitting.

Can I get insurance for a heavily modified car?

Yes, but not through mainstream price comparison websites in most cases. Heavily modified vehicles - particularly those with performance engine modifications, significant bodywork changes, or non-standard structural alterations - are underwritten by specialist FCA-authorised insurers accessible through BIBA-member brokers (biba.org.uk/find-insurance/). These insurers price individually based on the specific modifications declared and must comply with FCA Consumer Duty obligations.

Sources

• Consumer Insurance (Disclosure and Representations) Act 2012 - legislation.gov.uk/ukpga/2012/6
• Thatcham Research security device ratings - thatcham.org/vehicle-data/insurance-groups/
• DVSA MOT testing standards - gov.uk/get-your-vehicle-tested
• Road Traffic Act 1988 s.143 - legislation.gov.uk/ukpga/1988/52/section/143
• FCA Consumer Duty PS22/9 - fca.org.uk/publication/policy/ps22-9.pdf
• BIBA specialist broker finder - biba.org.uk/find-insurance/
• FCA Financial Services Register - register.fca.org.uk