Modifying a car can be a great way to improve its performance, look and sound. 

But some tweaks to your pride and joy - including fitting noisy exhaust systems, extreme dark-tinted windows, and number plate alterations - represent a hazard to other road users and can also affect a car’s overall safety. 

And when modifying a vehicle, it’s crucial you abide by the law - as you could get in trouble with the police if you don't.

But where in the UK are police forces having to work hardest to counteract illegal car modifications? 

At Select Car Leasing, we analysed Freedom of Information requests (FOIs) from 33 police forces to see which area had the highest number of reports, made by officers, for illegal vehicle modifications.

The stats cover a 12 month period spanning from August 2021 until August 2022.

All of the offences reported are likely to have resulted in either a fine, the possibility of 3 points on the driver’s licence, or the motorist being prohibited from driving until the modification had been removed. On-the-spot fines for incorrect - or missing - number plates, or excessively-loud exhaust systems - can reach £100. Fines for more serious offences can hit £1,000. 

Overall there were 10,498 illegal car modifications reported by forces across the UK, with the majority - 7,400 - of these being for illegal number plates. 

Areas with the Most Reported Illegal Car Modifications (2021-2022)

Avon and Somerset Police Area is UK's No.1 Illegal Car Modification Hot-Spot

Coming in with the most reported illegal modifications is the Avon and Somerset region – which covers areas such as Bath, Bristol and Taunton - with over 2,100 non-lawful modifications collared by cops.

The stats we've uncovered actually follow a report that 'noise detecting cameras' are being trialled in Bristol in an attempt to try and crack-down on 'boy-racers' making residents' lives a misery. 

Meanwhile number plate offences - 2,000 of them - were reported by police in the 12 month period. 

The county of Essex had the second highest incidence of illegal modifications, with 726 offences reported by police, including 567 number plates reported missing entirely, and 104 tinted windows reported for being too dark.

Rounding off the three areas with the most reports is Northern Ireland, with 641 reports - comprising 272 number plate infringements and 221 tinted windows breaking the law. 

Worst Performing Area in Each Category 

Area with the Least Reported Illegal Car Modifications

From the areas analysed, the police region with the least amount of illegal car modification reports is Cleveland – which includes areas such as Hartlepool, Middlesbrough and Redcar - with 24 reports, 22 number plates reported missing and only one bulb tint and one too-loud exhaust reported. 

Derbyshire has the second least reports, with 36 in total, 34 of which were for tinted windows being too dark.

From the ten areas with the least amount of reports, Dorset had the most reports for tinted windows, at 83 incidents, and the most reports for exhausts, at 38. 

North Yorkshire had the highest number of missing number plates with 113. Thames Valley had the most reports of illegal bulb tints at 23. 

Modifications and the Law

Number Plates

Updating a number plate is one of the easiest modifications to make, however, the rules are relatively strict with what is, and what isn’t, allowed.

Number plates must be clear and easy to read, following these rules:

• be made from a reflective material
• display black characters on a white background (front plate)
• display black characters on a yellow background (rear plate)
• not have a background pattern
• be marked to show who supplied the number plate
• be marked with a British Standard number - this is ‘BS AU 145e’ for plates fitted after 1 September 2021
• The characters must not be removable or reflective. If your number plates were fitted after 1 September 2021, they must also be a single shade of black

Number plates must show your registration number correctly. You cannot rearrange letters or numbers, or alter them so that they’re hard to read. The characters on a number plate need to be a certain height and size.

There are also laws around which flag is allowed and where it can be placed.

Failing any of these may result in a £1,000 fine and you could fail your MOT.

Tinted Windows

Tinted windows are the second most common reported modification on our list, with Norfolk having the most reports at 286.

Vehicles first used on 1 April 1985 or later:

The front windscreen must let at least 75% of light through and the front side windows must let at least 70% of light through.

Vehicles first used before 1 April 1985

The front windscreen and front side windows must both let at least 70% of light through.

If caught with windows which don’t let enough light through you could end up with a ‘prohibition notice’ stopping you from using your vehicle, or a penalty notice.

Exhausts

There are two main reasons why an exhaust might land you in trouble. 

Firstly, it's illegal to modify the exhaust system to make a vehicle noisier after it has been ‘type approved’ (checked it meets environmental and safety standards). The police can also take action, including handing-out a £50 on-the-spot fine, if your vehicle’s silencer doesn’t work in the way it was designed or if you’re driving in a way that creates too much noise. New cars produced since 2016 are legally not allowed to be louder than 72 decibels (dB)

The second reason an exhaust could be deemed illegal is if it fails the emissions test during an MOT. Vehicles found driving on releasing high levels of emissions on public roads could result in a £1,000 fine.

Bulb Tints

Bulb tints are the third most reported modification, with Essex having the most reported incidents, at 44 over the year.  

Whilst you can have bulbs with a slight blue tint to make them brighter, the tint can’t change the colour temperature above 4200K (Kelvin) as it will affect the light output. It’s also important to note that HID bulbs can only be used if they are factory-fitted. Headlights can be either white or yellow and rear lights are red. 

Conclusions

There are lots of modifications which can be made to a car, however, with fines of up to £1,000 and the potential to fail your MOT, it’s important to make sure you’re following the laws, too. 

With number plates, it’s important to keep the formatting the same as the factory-fitted one. 

The main concerns with exhausts are the amount of noise they produce and the amount of emissions. Front tinted windscreens must allow through 75% of light, and the front windows 70%. Bulbs mustn’t be too blue and must have a certain level of lumens.

Remember to always inform your insurance company of any modifications to your vehicle, otherwise, your insurance could be void.

When it comes to modifications made to a lease car - Select Car Leasing points out that if, on completion of a lease contract and return of the vehicle, the finance company needed to rectify any mods made, the customer would be liable for those costs.

If you're unsure about your options, have a chat with one or our expert leasing consultants. 

Methodology

FOIs from 33 police forces in the UK were analysed to find out the number of different mods that had been reported between August 2021 and August 2022. 

 Enjoyed this? Read our latest news:

• New Inception EV signposts the future of Peugeot
  
• Mercedes-Benz to launch its own EV rapid-charging network
  
• Isuzu D-Max named ‘Pick-up of the Year’
  
• Mazda MX-30 set for plug-in hybrid power
  
• Top 9 ways to make commuting more fun
  

Where To Next?

For all the latest reviews, advice and new car deals, sign up to our newsletter.

Looking for a great leasing deal? Check out our incredible range of special offers.

Read our latest reviews and find the right model for you.

Want to know more about leasing? Take a look at our comprehensive leasing guides.

Interested in everything motoring? Why not catch up on all the latest car leasing news.