Car Modding and UK Law

June 13, 2012


Getting involved with tinkering and upgrading technology can be great fun. If you like cars, then it is only natural you would want to make it truly yours. The laws on customisation that runs to more than a pair of furry dice can be a bit of a minefield though. Jamie Gibbs of (who have further advice on modified car insurance ) fills us in…

CC 'philcampbell' (Flickr)

Sometimes, having a bog standard, normal, ‘boring’ car just isn’t going to cut it, and you want to throw in some elbow grease and make it something much more unique. Modifying your car can give you a proper sense of individuality and, depending on how extravagant your modifications are, will be guaranteed to turn heads in your direction. Modified cars, however, are still a bit of a bugbear for many motorists because of the legal minefield they have to dodge to make sure their car it still roadworthy.

External modifications

CC 'lisadragon' (Flickr)

One of the most common ways that people tend to modify their cars is by tinting the windows. This might be because you want less eyestrain from the glare of daylight, because you want less UV light to tarnish your leather interior, or it might be because you want to feel like you’re a celebrity trying to dodge the paparazzi.

If you decide that you want a window tint modification, you need to make sure that it’s within the strict legal limits. The windscreen has to let in at least 75 per cent of light, and the front side windows have to let in at least 70 per cent of light in order to maintain adequate visibility. Most modern cars already have their windows slightly tinted, so adding any extra tint on top of this will in all likelihood breach the limits and it could lead to court action.

External modifications usually lead to the police taking an increased interest in you and your car. With ‘boy racer’ culture being a particular thorn in the law’s side, you might be tarred with the same brush for adding cosmetic mods to your car.

Performance modifications

For some, making the car look cool just isn’t enough, and they choose to go deeper and tinker with the insides. Lowering the suspension of the car seems to be a popular modification in order to improve handling, but lowering the car too much actually harms handling and the modified car becomes more unstable on less than perfect roads. It is recommended that the suspension is lowered no more than 30mm, otherwise you could compromise your handling.

Changing the exhaust system is also quite a popular modification, although there are strict limits regarding how much noise the exhaust makes. Any modified exhaust that emits a noise that is louder than the factory standard will be in breach of the law. It also has to be seen that your modified exhaust system is properly maintained and that it is in good working order.

(c) Tom Edge Photography - courtesy of Loxlee Loves Engines

Falling foul of your insurance

Even if your modified car is roadworthy and all the modifications are street legal, you might find yourself on the wrong side of the law because of invalidated insurance. Individual insurers can refuse to provide cover for a modified car, even if it counts as legal (engine remapping to give the car more power is an example of this). This is due to the car becoming an ‘unacceptable risk’ and so your insurance would be instantly cancelled if you have this. Bear in mind you are also obligated to inform your insurer about any modifications that you have on the car, so there’s no honest way you can dodge it.

Before you modify your car, always check with your insurer that it comes within your policy limits, and check how it will affect your premium. As a general rule, expect any modification you add to increase your car insurance premium, even cosmetic mods. Also, ensure that the modification is made by an approved body and a competent engineer. Cutting corners and allowing substandard work when pimping out your car can only lead to trouble.

What car mods do you wish you could install? Are fear over the law or insurance holding you back? Why not let us know in the comment section.

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  • Matt Hartwell

    I would very much like to gut a corsa and replace all the running gear and engine etc. with parts from a subaru, but alas I don’t think it’s legal. Highly unfair. :/