Modifying Your Car: What Is Legal and What to Tell Your Insurer

Most modifications are legal as long as the car still meets the road and MOT rules, but you must tell your insurer about any change from the standard specification. Some changes, such as a new colour or a different engine, also need to be reported to DVLA. Modifications rarely add value when you sell, and some will reduce it.

Which modifications are most common?

• Alloy wheels and different tyre sizes

• Lowered or uprated suspension

• Engine remaps and tuning boxes

• Aftermarket exhausts

• Body kits and spoilers

• Tinted windows

• Upgraded lights, audio or infotainment

What does the law say about modifications?

Any modified car still has to be roadworthy and meet the standards checked at the MOT. A few areas catch people out:

• Exhausts. It is illegal to modify an exhaust to make it louder, and a noisy or smoky exhaust can fail the MOT.

• Lights. Lights must be the right colour, correctly aimed and approved for road use. Some aftermarket headlight bulbs and coloured lights are not.

• Window tints. The windscreen must let at least 75% of light through and the front side windows at least 70%. Our window tint guide explains the limits.

• Number plates. Plates must meet the legal format, with no unofficial fonts or spacing. See our number plate guide.

When do I need to tell DVLA?

You need to update the details on your V5C log book if you change certain things about the car, such as the colour, the engine, the cylinder capacity, the fuel type or the body type. GOV.UK explains how on its page about changing vehicle details.

Do I need to tell my insurer?

Yes. Insurers generally expect you to declare any change from the manufacturer's standard specification, including cosmetic changes like alloy wheels. If you do not, the insurer may refuse to pay out or cancel your policy. Some modifications put premiums up, while some security upgrades may help.

Does a remap affect my warranty or insurance?

It can. A remap changes how the engine performs, and many manufacturer and used car warranties exclude engines that have been remapped. It must be declared to your insurer. Our remapping guide covers the pros and cons.

What should I check when buying a modified car?

• Were the modifications fitted professionally, and are there receipts?

• Does the seller know exactly what has been changed?

• Will the car pass its next MOT as it is?

• How much will it cost to insure with the modifications declared?

• Has it been driven hard, and is the service history complete?

Our used car buying checklist has more general checks.

Will modifications affect what my car is worth?

Usually they do not increase value, and many reduce the number of interested buyers. Subtle changes, such as manufacturer-style alloys or better infotainment, are least likely to put people off. Loud exhausts, heavily lowered suspension and engine tuning tend to narrow the market. Keeping the original parts so you can return the car to standard before selling can help.

Common questions

Are alloy wheels a modification for insurance?

Often, yes, if they are not the wheels the car was supplied with. Check with your insurer.

Can a modified car pass an MOT?

Yes, as long as the modifications do not stop it meeting the MOT standards, for example on lights, emissions, tyres and exhaust noise.

Do I need to tell DVLA about tinted windows?

No, tints are not recorded on the V5C, but they must still be within the legal limits for the windscreen and front side windows.

Selling or servicing a modified car in Barnsley

anycolourcar.com is based in Barnsley, South Yorkshire. To talk about selling your car, start at sell your motor or call sales on 01226 574410. For servicing or repairs, contact our service centre on 01226 574321. Our labour rate is £80 per hour plus VAT.

This guide is general information, not legal or financial advice. Updated October 2026.