Car Insurance for Modified Cars UK 2026

Last reviewed: 25 April 2026

What counts as a modification for insurance purposes

A modification for motor insurance purposes is any change to the vehicle from its original manufacturer specification as the vehicle left the factory. This definition is broader than most car owners assume, and many common changes are modifications that must be declared:

Performance modifications that insurers treat as high-impact: engine remapping or ECU tuning (increases power output beyond manufacturer specification); supercharger or turbo upgrades; exhaust system changes that alter performance; suspension lowering beyond manufacturer tolerance; brake upgrades; larger alloy wheels than factory specification (which change handling characteristics and tyre wear rates).

Appearance modifications with insurance impact: window tinting beyond the legal limits (front windscreen must transmit at least 75% of light; front side windows at least 70% under UK regulations); body kits and spoilers that alter aerodynamics and repair cost; non-standard paint colours; fitting of non-standard or after-market sound systems with significant value.

Modifications with minimal insurance impact: standard replacement of worn parts like-for-like; factory-optional features added during vehicle ownership; anti-theft security upgrades that reduce risk (may actually reduce premium).

Modifications the law requires disclosure of: the Road Traffic Act 1988 does not specifically mandate disclosure of modifications, but the Consumer Insurance (Disclosure and Representations) Act 2012 (CIDRA) requires policyholders to take reasonable care not to make a misrepresentation. An undisclosed modification that is material to the insurer's risk assessment constitutes a misrepresentation under CIDRA. If a claim arises and the insurer discovers an undisclosed modification, it may: void the policy from inception, reduce any claim settlement by the degree to which the non-disclosure affected the underwriting, or deny the claim entirely.

The CIDRA framework and what it means for modified car owners

The Consumer Insurance (Disclosure and Representations) Act 2012 replaced the common law duty of utmost good faith for consumer insurance contracts in the UK. CIDRA requires consumers to take reasonable care not to make a misrepresentation when applying for insurance, amending a policy, or renewing.

A modification that materially affects the risk -- such as an engine remap that increases power from 150bhp to 220bhp -- is a material fact. Failing to disclose it when asked (which all insurers do in the online quote process via "have you made any modifications") is a misrepresentation under CIDRA. The insurer's remedy depends on whether the misrepresentation was deliberate or careless.

A deliberate non-disclosure allows the insurer to void the policy and refuse all claims, retaining the premium. A careless (but not deliberate) non-disclosure allows the insurer to apply the remedy proportionate to what the underwriting decision would have been had the modification been disclosed -- which may mean reducing a claim settlement rather than voiding the policy entirely.

The safest approach is always full disclosure, even if the modification seems minor. Most insurers accept disclosed modifications; the premium adjustment for declaring them is far less consequential than a voided policy following a claim.

How modifications affect insurance groups and premiums

Insurance groups assigned by Thatcham Research are based on the vehicle as supplied from the factory. A significantly modified vehicle -- particularly one with performance enhancements -- may no longer correspond to its factory insurance group. Specialist modified car insurers re-assess the vehicle as modified and price accordingly.

Performance modifications typically increase the premium because they increase both the probability of a speed-related accident and the repair cost in the event of a claim. An engine remap alone can increase a premium by 15-50 percent depending on the insurer and the degree of performance increase.

Anti-theft modifications (immobilisers, tracking devices, upgraded alarm systems) can reduce the premium because they reduce theft risk. Thatcham Research grades security devices (Category 1-7) and insurers use these grades in pricing. A Thatcham Category 1 approved alarm and immobiliser may reduce the base premium by 5-10 percent.

Specialist modified car insurers

Mainstream direct insurers -- Admiral, Aviva, LV=, Direct Line -- will typically accept mild modifications (standard alloys within a size range, light exterior modifications) but may decline or heavily load significantly modified vehicles. For heavily modified vehicles -- including track-prepared road cars, extensively remapped engines, or vehicles with structural modifications -- specialist modified car insurers are the appropriate route.

Adrian Flux (confirm current FRN at register.fca.org.uk) is one of the UK's most established specialist modified car insurance brokers. Adrian Flux can place cover for vehicles that mainstream direct brands decline, including heavily modified road cars, track cars, and kit cars.

Footman James (confirm FRN at register.fca.org.uk) is a specialist classic and modified car insurer with particular expertise in agreed-value policies for modified vehicles.

Hagerty (confirm FRN at register.fca.org.uk) serves the specialist vehicle market including heavily modified cars and performance vehicles.

BIBA-registered specialist brokers (biba.org.uk/find-insurance/) with modified or performance car specialism provide access to the widest range of underwriters. For Lloyd's market capacity on the most extensively modified vehicles, a specialist broker is the only route.

Agreed value versus market value for modified cars

Standard motor insurance policies pay the vehicle's market value at the time of a total-loss claim. For a modified car, the market value as assessed by the insurer may not reflect the cost of the modifications -- because a standard valuation model prices the car at what the market would pay for an equivalent unmodified vehicle, not at the cost of building the modified specification.

An agreed value policy fixes the insured sum at an agreed amount at the start of the policy year, providing certainty that the payout on a total-loss claim will match the agreed figure (subject to policy terms). Specialist modified car insurers can arrange agreed value policies; mainstream direct brands typically cannot. For any modified vehicle where the modifications have added significant value, an agreed value policy is the appropriate product.

How modified car owners should approach the market

Step one: list all modifications from standard specification, however minor. Include engine tuning, suspension changes, exhaust modifications, wheel size changes, body kit additions, and any electronic modifications.

Step two: obtain quotes from mainstream direct insurers, disclosing all modifications. Some will accept mild modifications without excessive loading.

Step three: for significantly modified vehicles or where mainstream brands decline, contact Adrian Flux, Footman James, or a BIBA specialist broker. Provide a full modification list and, for high-value modifications, a professional modification assessment or photographic evidence.

Step four: if the modifications have added more than £2,000 in value to the vehicle, consider an agreed value policy from a specialist insurer to ensure total-loss payout reflects the actual insured value.

Track day insurance: a separate product from road motor insurance

Owners of modified performance vehicles frequently attend track days at UK circuits. Standard road motor insurance explicitly excludes use at race tracks, speed events, and competitive driving events. A modified car driven on a public road under a standard Comprehensive policy is not covered once it enters a track environment.

Track day insurance is a specialist single-day or multi-day product that provides cover specifically for track day use. It typically covers: accidental damage to the insured vehicle during track use, medical expenses for the driver, and third-party cover for damage to other participants' vehicles or circuit equipment (though terms vary significantly by provider). Third-party circuit damage cover is particularly important because circuit operators typically hold drivers personally liable for damage to barriers, gravel traps, tyre walls, and infrastructure.

Track day insurance providers include: Dayinsure (confirm FRN at register.fca.org.uk), Reis Motorsport Insurance, and several Lloyd's market specialist coverholders arranged through BIBA-registered brokers. Track day insurance is priced per day and per event. For a typical UK circuit day with a mid-range performance car, track day insurance costs broadly £80-£300 per day depending on vehicle value and circuit.

Heavily modified road cars -- which typically attend track days regularly -- should confirm with their standard road insurer that the road policy remains valid on public roads even when the vehicle is also used at track events. Some road insurers impose conditions on policies for vehicles that attend tracks, including requirements that the vehicle is returned to standard specification for track use, or that the policyholder discloses track day use when taking out the road policy.

Classic and modified car shows: agreed value and laid-up cover

Modified car owners who show their vehicles at concours, modified car shows, or motorsport events may encounter specific insurance considerations beyond standard road cover.

For vehicles that are stored between shows and driven infrequently on the road, a laid-up or stored vehicle policy provides cover during the storage period (fire, theft, flood, vandalism to the vehicle in storage) at a lower premium than a full road policy. Laid-up policies do not cover the vehicle for road use -- they are activated when the vehicle is declared off-road via SORN. The policy must be reinstated to a road-use policy before driving on public roads.

Agreed-value classic and modified car insurance, offered by Footman James, Hagerty, and specialist Lloyd's market coverholders, fixes the insured sum at a professionally assessed value. For a modified car whose value substantially exceeds its standard market value due to the modifications, agreed-value cover ensures a total-loss payout reflects the full insured value rather than the standard market value of an unmodified equivalent.

Key Figures

Frequently asked questions

Do I need to declare car modifications to my insurer?

Yes. All modifications from standard manufacturer specification must be declared as material facts. Failure to declare is a misrepresentation under the Consumer Insurance Act 2012 and can result in policy voidance and claim refusal.

Does a car modification always increase my premium?

Not always. Anti-theft security upgrades (Thatcham Cat 1 alarm) can reduce premiums. Performance modifications typically increase premiums materially. Mild appearance changes may have minimal impact if declared.

Which insurers cover modified cars?

For mildly modified vehicles, mainstream direct brands (Admiral, Aviva, LV=) will often accept cover with disclosed modifications. For heavily modified vehicles, specialist brokers including Adrian Flux, Footman James, and BIBA specialists are the appropriate route.

What is an agreed value modified car insurance policy?

An agreed value policy fixes the insured sum at a stated amount at policy inception, ensuring the total-loss payout reflects the agreed value including modifications rather than standard market value alone.

Is an engine remap a modification I need to declare?

Yes. An engine remap is a performance modification that must be declared. Undisclosed remaps are a common ground for claim refusal when discovered during investigation.

Sources and Verification

• Consumer Insurance (Disclosure and Representations) Act 2012: https://www.legislation.gov.uk/ukpga/2012/6
• gov.uk -- Vehicle window tinting: https://www.gov.uk/vehicle-approval/overview
• Thatcham Research -- Security grading: https://www.thatcham.org
• ABI Motor Insurance Premium Tracker Q4 2025: https://www.abi.org.uk
• BIBA -- Find a specialist broker: https://www.biba.org.uk/find-insurance/
• FCA Register: https://register.fca.org.uk
• HMRC IPT: https://www.gov.uk/guidance/insurance-premium-tax

This article is for informational purposes only and does not constitute financial advice. Always verify rates with official sources before making any financial decision.