Unlawful Modifications

From tinted windows to changing the colour of your lights – even removing the silencer from your exhaust – there are plenty of ways you can modify your vehicle.

But vehicle alterations can be very murky territory when it comes to your car insurance.

All modifications must be declared to your provider as they can have an impact on your premium. What’s more, some modification can even land you in hot water with the police, with hefty fines handed out even if changes were made before you bought the car.

We’ve requested data from each police force in the UK to see which parts of the country have fallen foul of some of the most common illegal modification laws in the last year.

The UK’s illegal vehicle modification hotspots

1. Gloucestershire
Population: 637,100
Total offences - 925
Offences per million people - 1,452

Once we take population size into consideration, it’s actually sleepy Gloucestershire in South West England which has the highest rate of unlawful modification fines, with an equivalent 1,452 offences committed per million people. The majority of these are related to modifications that obstruct the licence plate.

2. Norfolk
Population: 907,800
Total offences - 1,127
Offences per million people - 1,241

Second on the list is another more rural region in Norfolk, with 1,245 illegal modifications per million people, including the highest rate of those being stopped for offences related to exhausts, like removing the silencer.

3. Northern Ireland
Population: 1,893,700
Total offences - 2,232
Offences per million people - 1,179

Northern Ireland saw 2,232 total offences which was behind only London when it came to total offences and third when we take into account population size.

1. Gwent 
Population: 594,200 
Total offences - 4 
Offences per million people - 7 
At the opposite end of the spectrum, police in the Welsh county of Gwent recorded just four specified modification offences in the whole of last year. When set against its modest population of just under 600,000 people, it’s by far the area with the lowest proportion. 
2. Nottinghamshire 
Population: 1,161,100 
Total offences - 54 
Offences per million people - 47 
The area with the second-lowest number of unauthorised modifications was Nottinghamshire in the East Midlands, with just 47 per million people. Only two people were fined over the 12 months for not displaying the correct lights, while not a single person was fined for using tinted windows. 
3. Cambridgeshire 
Population: 855,800 
Total offences - 47 
Offences per million people - 55 
Cambridge Constabulary handed out just 47 fines for the offences that we specified, which equates to 55 per million people and makes it the area with the third-lowest number of fines.  

Unlawful modifications around the UK

The most common unlawful vehicle modifications

For the nation as a whole (excluding those authorities we didn’t hear back from), the majority of offences (56%) related to licence plates, with over 13,000 fines handed out in the last year.

This was followed by lights (5,723) and tinted windows (4,183) and, while they may cause us the most grief, there were only actually 776 offences relating to modified exhausts.

Brought to you by the car insurance experts at comparethemarket.com.


We issued a Freedom of Information (FOI) request to each police force in the UK, requesting the number of drivers who have been fined in breach of the below four offences during 2020. The data is based on the 36 forces who responded with the information:

  • Exhausts: The Road Vehicles (Construction and Use) Regulations 1986, Regulation 54
  • Lights: The Road Vehicles Lighting Regulations 1989, Regulation 11 
  • License Plate: The Road Vehicles (Display of Registration Marks) Regulations 2001, Regulations 5 & 6 
  • Tinted Windows: The Road Vehicles (Construction and Use) Regulations 1986, Regulation 32, Paragraph 10 

The data could have been sourced from a live operating system, reflecting on a specific moment in time and is subject to change as incidents are finalised. In other words, incidents may be initially recorded under a specific category but change with new information.  

Figures per million people were calculated using population figures from the Office for National Statistics’ crime in England and Wales: Police Force Area data tables as well as the population of Northern Ireland according to the Northern Ireland population mid-year estimate.