TVs or DVDs that can be seen directly or via reflection of the vehicle's driver are illegal.
Car horns must emit a uniform and continuous sound - not a tune or two-tone noise.
Spoilers must be safely and securely attached to the rear of the car. Additionally, they must not pose a visual obstruction to the driver via the rear view mirror.
Cars must let 75% of light through windscreens and 70% through front-side windows. Police can order you off the road until this is reduced. This may invalidate your insurance.
Increasing the noise of an exhaust is illegal and the police can act if they think it is causing alarm or distress.
Headlamps must be clearly white or yellow. Ice cool blue tints that are too severe are illegal and will result in the police pulling you over.
All numbers and letters must be kept at standard size. National flags can be used in design, but no other symbols are permitted. If plates are incorrectly displayed, you may face a fine of up to £1000.
Whilst these lights are not always illegal, police may still pull you over depending on the brightness, as they may be considered too distracting for other road users.
All four tyres must be compatible with each other. They must be inflated to manufacturer's specifications, fit for purpose and in good repair.
Altering a car's suspension too much can adversely affect road-handling, making it both dangerous and unlawful.