Not all modifications affect your car insurance the same way. Power-increasing modifications typically raise premiums by 20–150%, while safety upgrades can reduce them by 5–15%. What matters most to insurers is not the cost of the modification, but how it changes the car’s probability of a claim. Failing to declare any modification — regardless of cost — can void your policy.

Modifications That Increase Premiums

These modifications signal higher risk to insurers and will raise your premium:

Modifications That Can Reduce Premiums

A smaller number of modifications actually reduce risk in insurers’ eyes:

• GPS tracking device (Thatcham-approved): up to −10%
• Dashcam: −3–5% with some insurers
• Roll cage with harness: some motorsport specialists offer reductions for properly installed HANS-compatible setups
• Immobiliser upgrade: −2–8% for Thatcham Category 1 devices

Modifications That Must Be Declared (Even If They Seem Minor)

Insurers require disclosure of any modification that differs from the manufacturer’s original specification, including:

• Tinted windows
• Sound system upgrades
• Aftermarket steering wheel
• Custom paint or vinyl wrap
• Non-standard seats
• Short-throw shifter
• Performance air filter (even a drop-in panel filter)

What Happens If You Don’t Declare?

Non-disclosure is treated as material misrepresentation. At claim time, insurers conduct a thorough inspection. If undeclared modifications are found, the insurer can void the policy from inception — meaning you receive nothing, and you may face liability for third-party costs. With specialist modified car insurers, declaring upfront almost always produces a better outcome than hiding mods and losing a claim later.

Track Use and Its Impact

Adding track use — even occasional circuit days — to your policy is a modification to the policy’s permitted use. This must be declared separately from physical modifications. Track use typically adds 15–40% to your annual premium. Use our insurance estimator to model the combined effect of your modifications and track use on your quote.