Legal or Not? Tuning Mods That’ll Get You an MOT Fail or Pulled Over

Fast, Loud, and… Illegal?

You’ve bolted on a quad exhaust, blacked out your windows, and dropped the car so low it looks like it’s vacuuming the tarmac. It looks proper. But is it legal?

When it comes to modifying your car in the UK, there's a fine line between stylish and straight-up illegal. Some mods might get you a nod from the local car club, but a big shake of the head from your MOT tester—or worse, the police.

Let’s break down the most common mods and where they stand in the eyes of the law. No fluff. Just facts.

1. Exhaust Systems – Mind the Noise

Legal limit: 74 decibels for most vehicles. Anything louder can land you in hot water.

What’s illegal?

• Decat pipes (removing the catalytic converter)
• Straight pipes without silencers
• Popping, banging “flame maps” that trigger noise complaints

TVP Tip: Stick with our aftermarket exhaust tips and quad diffuser setups. You get the sporty look without attracting attention from noise cameras or roadside testers.

2. Window Tints – The Front-End Trap

Rules:

• Front windscreen must let in 75% light
• Front side windows must let in 70%
• Rear windows? Go as dark as you like.

Fail Warning: If your front windows are too dark, it’s an MOT fail AND points on your licence—not to mention a fine if you get stopped.

3. Lighting Mods – Cool or Caution?

Underglow lights? Legal… ish.

• Must not flash or be red/blue
• Can’t be visible from the front or rear while driving
• Only for shows and static displays
  
  

Other lighting laws:

• Headlight tinting is illegal if it reduces light output
• Aftermarket DRLs or LED bulbs must be E-marked and properly aligned
• Rear lights must remain red—no smoked-out nonsense if it affects visibility

4. Number Plates – Fonts, Spacing, and Show Plates

Custom plates can look mint. But mess with:

• Font style
• Spacing
• Bolts to “spell” words
• Colouring

… and you’re asking for a pull. Plates must be BS AU 145e compliant, with a maker’s mark, and the right reflective material. Show plates? Track only. Not for road use. Ever.

5. Suspension Mods – Slam It… But Not Too Hard

Coilovers, air suspension, and lowering springs? All legal if:

• Your tyres don’t rub
• Your lights aren’t misaligned
• Your number plate isn’t scraping the ground

But go too low and you risk:

• MOT failure
• Handling issues
• Insurance refusal if not declared

6. Air Filters and Induction Kits – Mostly Legal (With a But)

Swapping out your factory airbox for a high-flow cone filter? Totally fine if it doesn’t:

• Trigger the check engine light
• Bypass sensors
• Cause excessive noise

Heat shielding is a must—hot air intakes can reduce power and draw unwanted attention during emissions tests.

7. Spoilers, Lips & Diffusers – Style Without Risk

These mods are mostly cosmetic. But if you go mad with bolt-on wings or splitter setups:

• They can be illegal if they project dangerously
• Can fail MOT if they obstruct your lights or plate
• Might be flagged if they aren’t secure

TVP Range: All our styling parts are made to fit properly. From M-look rear diffusers to GTI-style front lips, they keep your car legal and lethal-looking.

8. The Grey Area – Legal (But Risky)

Mods that might technically be road-legal, but can still get you pulled, flagged at MOT, or cause insurance issues.

Examples:

• Loud dump valves
• Pops & bangs from remaps
• Stretch tyres
• “Legal” tints that look dodgy

9. Insurance – The Big One Everyone Ignores

Even if your mods are 100% legal, your insurance can be void if you don’t declare them.

Yes, even little things:

• Aftermarket wheels
• Tinted lights
• Remaps
• Upgraded brakes
  
  

If in doubt: declare it. A non-declared £50 mod could invalidate a £10k claim.

Final Takeaway: Mod Smart, Not Dodgy

If it sounds too good to be true, or too loud to be legal—it probably is. Keep it smart, keep it safe, and keep it roadworthy.

At Trade Vehicle Parts, we stock legal styling upgrades and performance mods that won’t get you flagged at your MOT or pulled by the local bobbies.

Pop in your reg, and we’ll show you what fits — and what’s fit for the road!