Introduction: A Clear Guide to a Common Modification

Aftermarket mudflaps are both a practical shield against road grime and a key cosmetic statement for rally-inspired vehicles. However, despite their popularity, users aren’t always sure of their legal status. Drivers are often confused about the rules and, more importantly, their contractual obligations to their insurer.

This guide separates fact from fiction, looking at UK construction laws, official MOT inspection standards, and the non-negotiable rules set by insurance providers.

Before we dive in, here are the short answers:

• Are they legally required? No. UK law does not require passenger cars to be fitted with mudflaps.
• Are they legal to fit? Yes, as long as they are installed safely: secure, with no sharp edges, and not interfering with the wheels.
• Will they fail an MOT? A car will not fail for lacking mudflaps. It can fail if a fitted mudflap is insecure, sharp, or rubbing against the tyre.
• Must I declare them to insurance? Yes, absolutely. This is critical. An aftermarket mudflap is a “vehicle modification,” and failing to declare it can void your policy.

Are mud flaps required by law in the UK?

The simple answer is no. For a standard private passenger car (M1 category), no specific UK law mandates the fitting of mudflaps.

The common confusion on this point comes from rules that apply to entirely different vehicles.

The Source of Confusion: The HGV “Spray Suppression” Law

The primary legislation covers these regulations, including details on “Spray suppression devices“.

This technical rule mandates specific spray-suppression equipment, but it only applies to heavy goods vehicles (HGVs) over 12,000 kg and large trailers. This is why lorries have complex, bristly flaps—they are a legal requirement for them, not for you.

The Law That Does Apply to Passenger Cars: Regulation 63

The C&U regulation for passenger cars is found here.

This law simply states a vehicle must have “wings or other similar fittings to catch, so far as practicable, mud or water thrown up by the rotation of its wheels”. In any modern car, the standard factory-fitted wheel arch and its liner are legally considered the “wing” that satisfies this requirement.

Therefore, you are not breaking the law by not having mudflaps. Fitting them is simply an enhancement to your car’s existing compliance.

Are mud flaps legal?

Yes, fitting aftermarket mudflaps is perfectly legal, provided they are installed in a way that doesn’t make the vehicle unsafe.

Their legality is governed by the general C&U regulation that prohibits any vehicle from being used in a “dangerous condition”. To ensure your mudflaps are legal, they must be:

1. Securely Fastened – The modification must be “fastened safely”. An MOT can fail a wheel trim if it’s “insecure” or “detachment is imminent”, and this principle applies directly to mudflaps. A loose flap is illegal because it could detach and strike another road user.
2. Free from Sharp Edges – The rules for spoilers and wheel trims are explicit: they are illegal if they have “exposed sharp edges… likely to cause injury.” If a rigid plastic mudflap cracks, it may create a jagged edge, making the vehicle illegal to use.
3. Clear of Moving Parts – This is important. It is illegal for tyres to “rub on the body work or mechanics of the vehicle”. If you fit oversized “rally-style” flaps, especially on a lowered car, they may “foul” (rub) the tyre on a full steering lock or when the suspension compresses. This is dangerous and can lead to a tyre blowout, so checking the fitment once mudflaps are installed is critical.

There is a subtle distinction between the law (C&U) and the MOT test. The C&U regulations are enforced by the Police at all times, while the MOT is just a periodic inspection of specific items. A securely fitted mudflap actually strengthens your compliance with the spirit of the C&U regulations by catching spray.

Do you need mudflaps to pass an inspection?

No. A vehicle will not fail its MOT for the simple reason of not having mudflaps fitted.

Analysis of the MOT Manual

The MOT inspection manual for private passenger and light commercial vehicles does not list “mudflaps” as a specific testable item for passenger cars.

How Aftermarket Mudflaps Can Cause an MOT Fail

This is the key takeaway. While the MOT tester won’t look for mudflaps, they will inspect them if they are fitted. A fitted mudflap is part of the car’s “Body, structure and attachments”, and if it’s unsafe, it will fail.

There are three primary ways your mudflaps can cause an MOT fail:

1. Fouling the Tyre: The tester will check if the tyre can touch any part of the vehicle.
   • MOT Manual Reference: https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/5-axles-wheels-tyres-and-suspension
   • Failure Criteria: “A tyre is fouling a part of the vehicle at the time of test”. This is a Major or Dangerous defect.
2. Being Insecure: The tester will physically check if components are safely attached.
   • MOT Manual Reference: https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/6-body-structure-and-attachments, by analogy.
   • Failure Criteria (Analogue): “A body panel… insecure” (Major defect) or “likely to become detached” (Dangerous defect).
3. Having Sharp Edges: The tester will assess the bodywork for injury risk.
   • MOT Manual Reference: https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-and-light-commercial-vehicles/6-body-structure-and-attachments
   • Failure Criteria (Analogue): “A body panel… damaged… and likely to cause injury“. A cracked, rigid mudflap falls into this category (Major defect).

How Aftermarket Mudflaps Can Fail Your MOT

To pass, fit your mudflaps securely, check for tyre clearance at full steering lock, and ensure they are not loose.

Do you need to declare mudflaps?

Yes. Absolutely and without exception. You must declare aftermarket mudflaps to your car insurance provider.

What is a “Modification” to an Insurer?

To an insurer, a modification is any change made to a vehicle that was not part of the manufacturer’s original factory specification.

This definition is contractual, not based on performance. It includes cosmetic items like stickers, different wheels, and aftermarket mudflaps.

The Risk of Not Declaring

If you are in an accident, your insurer will send an assessor to inspect your vehicle. If they find any undeclared modification—even minor ones like mudflaps—they have the contractual right to void your entire policy.

This means they will not pay for your repairs, the other party’s damages, or any personal injury claims, leaving you personally liable for all costs. Failing to declare a mod is considered misrepresentation or insurance fraud.

Will Declaring Mudflaps Increase My Insurance Premium?

This depends entirely on your insurance provider.

• Why they might charge more: Some insurers’ algorithms associate any modification with a higher-risk driver profile, increased theft risk, or slightly higher repair costs.
• Why they might not: Many reputable insurers (like The AA) make exceptions for practical modifications that don’t increase risk, such as tow bars or parking sensors. A strong argument can be made that mudflaps, which protect bodywork, fall into this “practical” category.

When you call to declare them, one of three things will likely happen:

1. No Change: Many specialist insurers will simply add the modification as a note on your policy.
2. A Minor Fee: Some may charge a small admin fee or a minimal premium increase.
3. Refusal to Cover: Some risk-averse insurers do not cover any modified cars.

Expert Recommendation:

Always check with your insurer before you fit the part. If they want to charge a large amount or refuse cover, shop around for a “modified car insurance” specialist, who will likely cover the mudflaps for little or no extra cost.

Conclusion: A Summary for Safe Modifying

To stay legal, safe, and insured, follow these four rules:

1. Legality (Requirement): You are not legally required to have mudflaps on a passenger car. Your car’s factory wheel arches already satisfy C&U https://www.legislation.gov.uk/uksi/1986/1078/regulation/63
2. Safety (Legality of Fitment): Your fitted mudflaps are legal only if they are securely fastened, free from sharp edges, and do not rub against the tyres.
3. MOT Inspection: An MOT will not fail your car for lacking mudflaps. It will fail if your fitted mudflaps are insecure, sharp, or fouling the tyres.
4. Insurance: You must declare aftermarket mudflaps to your insurer as a “modification”.Failing to do so can void your entire policy.

Now that we have cleared up the legal, MOT and insurance status of mudflaps, and determined that they are legal, let’s find out whether it is worth putting mudflaps on a car.