If your car has been modified in any way you may find that most insurers will refuse to cover it. This is because those modifications might well have either made the car less safe, or more powerful. Unless alteration work on a car is carried out by a properly qualified and experienced person there is a danger that the structure can be weakened, or safety features that have been designed into the structure, such as crumple zones to protect occupants or pedestrians, can be compromised.
Flared mudguards may look striking; but they can cause serious injury if they hit a pedestrian. Raising or lowering the height of the bodywork can upset the steering geometry on the road holding. A bigger engine may provide more power than the braking system can handle. Even adding extra mirrors to a car can cause hazards in the event of a collision. These are reasons why insurance companies are very wary of modified cars.
There are modifications however that are essential or desirable. Alterations can be made in order to accommodate the needs of a disabled driver; or a fuel system can be switched from petrol to liquefied gas. These alterations would not normally cause any, or at least very little, increase in premium. However it is essential that if they are carried out the insurance company is kept fully informed so that they can be confident that the work is being carried out in an efficient manner.
Modern cars are very carefully designed to have good road holding, steering and braking. The bodies of our cars are designed to offer the least possible danger to the driver, passengers, or any other person in the event of an accident. Interfering with any of these factors could possibly make the car more dangerous, and therefore increase the possibility of a claim. This is why it is quite reasonable for insurers to treat modifications with considerable scepticism.
If your car is modified in any way it will be necessary for you to show that these modifications have not affected the safety of the vehicle in any way, and have not made it more powerful or faster. This is another of those areas in which professional advice from an experienced broker will be essential.