How Car Modifications Affect Your Insurance in the UK

Summary

• You must declare all modifications: Even cosmetic changes. Failing to declare voids your policy.
• Most mods increase premiums: Performance upgrades have the biggest impact.
• Some mods can reduce premiums: Security upgrades like trackers and immobilisers may help.

Modified your car or thinking about it? Your insurance company needs to know. And yes, it will probably affect your premium.

This guide explains which modifications matter, how much they cost, and how to avoid accidentally voiding your cover.

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What Counts as a Modification?

A modification is anything that changes the car from its factory specification. This includes:

Performance Modifications

• Engine remapping or ECU tuning
• Turbocharger or supercharger
• Air intake and exhaust upgrades
• Sports suspension (lowered or coilovers)
• Uprated brakes

Cosmetic Modifications

• Body kits and splitters
• Aftermarket alloy wheels
• Window tinting
• Vinyl wraps or custom paint
• Interior changes (seats, steering wheel, roll cage)

In-Car Modifications

• Aftermarket stereo or speakers
• Sat nav upgrades
• Dashcam (usually fine but worth declaring)

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Why You Must Declare Modifications

This is not optional. It's a legal requirement.

• Undeclared modifications void your policy. If you claim, the insurer can refuse to pay.
• You could face prosecution. Driving without valid insurance is a criminal offence.
• Points and fines: 6–8 penalty points and an unlimited fine for no insurance.

Important: Even if the modification was done by a previous owner, you must still declare it. If in doubt, declare it.

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How Modifications Affect Your Premium

Modification	Typical Premium Impact
Engine remap	+15–30%
Turbo/supercharger	+30–50%
Lowered suspension	+10–20%
Body kit	+10–25%
Aftermarket alloys	+5–15%
Window tinting	+0–10%
Tracker fitted	-5–15% (can reduce)
Upgraded alarm	-5–10% (can reduce)

Performance mods cost most because they increase the car's speed, power, and accident risk.

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Modifications That Can Reduce Your Premium

Not all mods increase costs. Security upgrades can actually save you money.

• Thatcham-approved alarm: Many insurers give discounts for approved alarms.
• GPS tracker: Makes your car easier to recover if stolen. Some insurers require one for high-value cars.
• Immobiliser upgrade: Prevents the engine from starting without the correct key.
• Dashcam: Some insurers offer small discounts for dashcam users. It also helps in the event of a claim.

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Finding Modified Car Insurance

Not all insurers cover modified cars. Here's how to find the best deal.

1. Use specialist brokers: Companies like Adrian Flux and Keith Michaels specialise in modified car insurance.
2. Be upfront about every modification. List everything, even small changes.
3. Get multiple quotes. Prices vary hugely between insurers for modified cars.
4. Join an owners' club: Some clubs have insurance deals with specialist providers.
5. Consider agreed value policies. These set a fixed payout value, which makes sense for heavily modified cars.

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What Happens If You Don't Declare Modifications?

The consequences are serious. Don't risk it.

1. Claim refused: Your insurer can refuse to pay any claim if modifications are undeclared.
2. Policy cancelled: Your policy is voided. This goes on record and makes future insurance much harder to get.
3. Criminal prosecution: Driving without valid insurance carries 6–8 penalty points and an unlimited fine.
4. Car seized: The police can seize and crush an uninsured vehicle.

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If you modify your car, declare it. It's not worth the risk of an undeclared modification voiding your insurance. Shop around with specialist brokers to find the best deal for your modified ride.

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