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Modified car insurance 

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1Accurate as of January 2023.

What is modified car insurance?

Modified car insurance is what you take out to cover your car if you’ve had it altered in any way. It’s a standard car insurance policy, however, the premiums will also factor in any changes that have been made to the vehicle..

This is why if you do make any custom changes – or you purchase a vehicle that has been customised from the factory model – you should let your insurance provider know. Failure to do so could result in your policy being invalid when you come to make a claim.

How does modified car insurance work?

If you have your heart set on modifying your car, then you should always consult your insurance company before you do anything. They can tell you what impact, if any, the changes will make to your policy and premiums. You can then weigh up whether any modifications are worth the increase in insurance costs.

Insurers allocate each car to one of 50 car insurance groups (one is the cheapest and 50 the most expensive). If the specifications of your car have changed, the vehicle no longer conforms to their analysis, and the rating is void. Insurers’ logic is that modification work done on the structure or mechanics of a car outside the factory cannot be guaranteed, and that it might compromise the integrity of the vehicle.

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What counts as a car modification?

The most popular car modifications in the UK are alloy wheels, suspension changes and exhaust system changes. Other common customisations include tinted windows, tow bars and engine management systems.

Modifications such as  personalised number plates may not directly affect your car insurance premium, but you will need to notify your insurer if you make them, and an admin fee may be charged to update your records.


What is covered by modified car insurance?

Insurance policies for modified cars offer everything you’ll get with most car insurance policies – depending on the level of cover you take out, you should be able to get cover for:

  • Your vehicle

    A fully comprehensive car insurance policy should provide cover for you and your vehicle against a range of insured events, including fire, theft, and more

  • Modifications

    This cover will also extend to any modifications you’ve had made or installed – so long as you’ve declared them to the insurer

  • Third-party damage

    You’ll also be covered for any damage you do to a third party, their vehicle, or their property

  • Any extras you choose

    Car insurance policies also offer a range of extra features like car key cover and windscreen cover – some are included as standard, while others are usually available at an extra cost

Why are modified cars more expensive to insure?

The main reason why your insurance premiums could go up is increased risk.

Insurance companies calculate their prices using statistics, and because motorists using high-performance vehicles are more likely to be involved in a crash – and many modifications improve a vehicle’s performance – insurers believe their premiums should be higher. 

Modifying your vehicle introduces an element of uncertainty because the insurer is not 100% sure of the workmanship or what specifically has been done. They mitigate this uncertainty by putting up the cost of cover. 

Modified vehicles are also often more attractive to thieves, and are therefore at greater risk of being stolen, which also increases your premium. 

Car modifications don’t have to be significant to affect your insurance, for example adding things like entertainment systems and parking sensors.

Below are the different categories of modifications you can declare when comparing policies through MoneySuperMarket, and the average annual premiums for drivers with these modifications included.

Category of modification

Average annual premiums*



Engine transmission


Wheels and tyres 


Suspension and steering


Spoiler and body-kit






Body modifications


*Based on fully comprehensive car insurance policies with one driver holding a full UK driving licence. MoneySuperMarket data collected between May 2021 and April 2022.

How to get cheaper modified car insurance cover?

If you’ve had your car modified, you might want to consider the following to help balance the higher insurance costs:

  • 1

    Paying annually

    Paying your car insurance premiums annually usually works out cheaper than spreading the cost over 12 months

  • 2

    Volunteering a higher excess

    Paying a higher voluntary excess tells insurers you’re unlikely to bother with small claims that wouldn’t be worth the cost

  • 3

    Build a no-claims discount

    If you can go for over a year without claiming you’ll start to accumulate a no-claims discount on future premiums

  • 4

    Reduce your mileage

    The less time you spend on the road the lower your chances of being involved in an accident, so giving a lower estimated mileage can cut your premiums

  • 5

    Consider pay-as-you-go:

    Pay-as-you-go car insurance lets you pay for cover either by-the-mile, by-the-hour or based on your driving, and can be a cheaper alternative for some drivers

  • 6

    Avoid auto-renewing

    You might be able to find a cheaper deal on your car insurance if you compare quotes rather than auto renewing your policy

Car insurance is almost always more expensive for younger drivers, and this is true for modified cars too. Unfortunately for young drivers, they are associated with a higher claim risk due to their inexperience on the road – as a result, insurers charge higher premiums.

If you’ve modified a car after purchasing it, you just need to inform your insurer of all the work that has been done to the car so they can factor it in when deciding your premiums.

Not all modifications push up car insurance premiums. If you install additional security measures to prevent your car from being stolen, such as an alarm, you may see your premiums fall because your provider considers you a lower risk.

The same holds true for immobilisers and tracking devices but call your insurer to check whether a reduction will be made and how much it will be.

You can customise your vehicle whenever you choose, but you must notify your insurance company who will then decide on how the modifications affect your premiums. 

The important thing to understand is that the existing insurance policy covers your car for its original condition. Once that is changed, the policy needs to be adjusted to suit or you risk invalidating the insurance.

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