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Modified Car Insurance: What You Need to Declare

Any modification to your vehicle — whether it makes it faster, looks different, or improves security — should be declared to your insurer. Not doing so could invalidate your policy. Here's how modifications affect your insurance.

"Will a security modification like a Ghost Immobiliser lower or raise my premium?"

Why Do Modifications Affect Insurance?

Insurers assess risk based on the vehicle as it was originally manufactured. Any change from the factory specification — whether performance, cosmetic, or security-related — alters the risk profile of the vehicle and needs to be taken into account.

Modifications that increase performance or value typically increase premiums. Modifications that improve security may, in some cases, help reduce premiums — though this varies by insurer.

Types of Modification and Their Typical Impact

Modification typeExamplesTypical premium impact
PerformanceEngine remapping, turbo kits, exhaust upgrades, air filtersUsually increases premium
CosmeticBody kits, spoilers, alloy wheels, tinted windows, wrapsMay increase slightly; varies by insurer
Audio / ICEUpgraded stereo, subwoofers, screensMay increase (higher replacement value)
SuspensionLowered suspension, coilovers, upgraded springsUsually increases premium
SecurityGhost Immobiliser, Thatcham-rated tracker, steering wheel lockMay reduce premium with some insurers
AccessibilityWheelchair lifts, hand controls, adapted steeringTypically neutral; specialist policies available

Premium impacts are general indications. Actual effects vary by insurer, vehicle, and individual circumstances.

Do Security Modifications Reduce Premiums?

This is one of the most common questions from modified car owners. The answer is: they can, but it's not guaranteed.

Security modifications like a Ghost Immobiliser, Thatcham-rated tracker, or steering wheel lock reduce the risk of theft. Some insurers recognise this and may offer lower premiums as a result. However, others may treat any modification as a deviation from factory specification and not adjust the price downward.

The best way to find out is to compare quotes with your security modifications declared. You may find that some insurers offer noticeably better prices than others when security devices are fitted.

Worth knowing: Thatcham Research rates security devices on a scale. Devices rated by Thatcham are generally more widely recognised by insurers. If you're fitting a security device specifically to reduce your premium, check whether it has a Thatcham rating.

What Happens If I Don't Declare a Modification?

You must declare all modifications when taking out or renewing your car insurance. Failing to do so can have serious consequences:

Important: "Modification" has a broad definition in insurance terms. It includes anything that changes the vehicle from its original factory specification — even changes that seem minor, such as aftermarket alloy wheels, a roof rack, or a dashcam hardwired into the vehicle's electrics.

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Modified Car Insurance FAQs

Will a Ghost Immobiliser lower my car insurance?
It may do with some insurers, as a Ghost Immobiliser reduces the risk of theft. However, not all insurers adjust premiums for aftermarket security devices. The best approach is to declare it when comparing quotes and see how different insurers price it.
Do I have to declare a dashcam as a modification?
If the dashcam is a portable, plug-in device, most insurers don't consider it a modification. However, if it's been hardwired into the vehicle's electrics, some insurers may classify it as a modification. When in doubt, declare it.
What's a Thatcham rating and does it matter for insurance?
Thatcham Research is an independent organisation that rates vehicle security products. A Thatcham-rated device has been independently tested and certified, which is generally more widely recognised by insurers than unrated products.
Can I get an agreed value policy for a modified car?
Some insurers offer agreed value policies, where you and the insurer agree on the vehicle's value upfront. This can be useful for heavily modified vehicles where the market value may not reflect the cost of the modifications. Not all insurers offer this, so it's worth checking when comparing.

General information only. Not financial advice. Always declare all modifications and read policy terms before purchasing.

*51% of consumers could save £535.17 on their Car Insurance. The saving was calculated by comparing the cheapest price found with the average of the next four cheapest prices quoted by insurance providers on Seopa Ltd's insurance comparison website. This is based on representative cost savings from May 2026 data. The savings you could achieve are dependent on your individual circumstances and how you selected your current insurance supplier.

** Correct as of June 2025.

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