What Part of the Car Does the Law Require You to Keep in Good Condition?

UK law requires drivers to keep every safety-critical part of their car in good condition whenever it is used on public roads.

This includes the tyres, brakes, steering, lights, indicators, mirrors, windscreen, wipers, washers, seat belts, suspension, exhaust system, emissions equipment and number plates.

The law does not apply to only one part of the car. The whole vehicle must be roadworthy. GOV.UK states that drivers are responsible for making sure their vehicle is always safe to drive, and that a vehicle can be unsafe even if it has a current MOT certificate.

Driving a vehicle in a dangerous condition can lead to a fine of up to £2,500, a driving ban and 3 penalty points.

Quick Answer: Which Parts of a Car Must Be Kept in Good Condition?

The main parts of a car that must be kept in good condition by law are:

• Tyres
• Brakes
• Steering
• Lights
• Indicators
• Windscreen
• Wipers
• Washers
• Mirrors
• Seat belts
• Suspension
• Exhaust system
• Emissions equipment
• Number plates

These parts matter because they affect braking, control, visibility, passenger safety, pollution control and vehicle identification. If any of these parts become defective, the car may be unsafe or illegal to drive.

Key Takeaways

• UK drivers must keep their vehicle roadworthy every time it is driven.
• A valid MOT certificate does not guarantee the vehicle remains legal for the full year.
• Tyres, brakes, steering, lights and visibility equipment are among the most important legal safety items.
• Cars, light vans and light trailers must have at least 1.6mm tyre tread depth across the central three-quarters of the tread and around the full circumference.
• Incorrectly displayed number plates can lead to a fine of up to £1,000 and MOT failure.
• Drivers should carry out regular safety checks instead of waiting for the annual MOT.

Why This Question Matters for UK Drivers?

Many UK drivers assume that once a car has passed its MOT, it is legally safe for the next 12 months. That is not correct.

An MOT is only a test of the vehicle’s condition at the time of inspection. A tyre can become illegal after the MOT. A brake light can fail the next day.

A windscreen crack can spread. A number plate can become unreadable. If the vehicle becomes unsafe, the driver remains responsible.

This is why roadworthiness is an ongoing legal duty. It applies every time the vehicle is used, whether the journey is long or short.

What Does UK Law Say About Vehicle Roadworthiness?

UK roadworthiness rules are based on the principle that vehicles used on public roads must not create danger for the driver, passengers, pedestrians, cyclists or other road users.

The Road Traffic Act 1988 makes it an offence to use, cause or permit the use of a vehicle or trailer in a dangerous condition. The practical meaning is that drivers must not drive a car if its condition creates a danger of injury.

GOV.UK also confirms that drivers can be fined, banned and given penalty points for driving a vehicle in a dangerous condition.

For everyday motorists, this means a car should be maintained so that it can be driven safely, controlled properly, seen clearly by other road users and identified correctly by its registration plates.

What Does “Good Condition” Mean for a Car?

In simple terms, “good condition” means the vehicle is safe, roadworthy, legal and fit to be used on public roads.

A car in good condition should:

• Stop safely when the brakes are used
• Steer correctly without looseness or stiffness
• Have tyres with legal tread depth and no dangerous damage
• Have working lights and indicators
• Give the driver a clear view through the windscreen and mirrors
• Have working wipers and washers
• Have secure and functioning seat belts
• Have number plates that are clean, readable and correctly displayed
• Not produce excessive smoke, noise or emissions
• Not have dangerous suspension, exhaust or structural defects

A car does not need to be perfect or brand new to be legal. However, it must not have defects that make it unsafe, unroadworthy or non-compliant with legal requirements.

Main Car Parts That Must Be Legally Maintained

The table below explains the main car parts drivers must keep in good condition and why they matter.

Car Part	Legal Importance	Common Problems
Tyres	Grip, braking, steering and stability	Low tread, cuts, bulges, wrong pressure
Brakes	Safe stopping distance and control	Worn pads, brake fluid issues, pulling to one side
Steering	Directional control	Stiff steering, loose steering, vibration
Lights	Visibility and signalling	Failed bulbs, poor alignment, dirty lenses
Indicators	Communicating direction changes	Faulty bulbs, fast flashing, no signal
Windscreen	Clear view of the road	Cracks, chips, obstruction, heavy dirt
Wipers	Clearing rain and debris	Smearing, splitting, poor contact
Washers	Cleaning the windscreen	Empty washer fluid, blocked jets
Mirrors	Rear and side visibility	Broken glass, missing mirror, poor adjustment
Seat belts	Occupant protection	Fraying, faulty latch, poor retraction
Suspension	Stability and handling	Broken springs, worn shock absorbers
Exhaust	Noise, emissions and fumes control	Leaks, excessive noise, smoke
Number plates	Vehicle identification	Dirty, cracked, altered or incorrectly spaced plates

Are Tyres the Most Important Legal Part of a Car?

Tyres are one of the most important legal parts of a car because they affect grip, braking, steering and stability.

For cars, light vans and light trailers, the legal minimum tyre tread depth is 1.6mm across the central three-quarters of the tread and around the entire circumference.

Tyres should also be:

• Properly inflated
• Free from bulges
• Free from exposed cords
• Free from serious cuts
• Suitable for the vehicle
• Correctly fitted
• Evenly worn

Illegal tyres are a serious offence. The official THINK! road safety campaign warns that drivers stopped with illegal tyres could receive a £2,500 fine and 3 penalty points per tyre.

How to Check Tyre Tread Depth?

Drivers can check tyre tread with:

• A proper tyre tread depth gauge
• Tyre tread wear indicators
• The common 20p coin check as an informal guide

A tread depth gauge is the most accurate option. The 20p check can be useful for a quick visual check, but drivers should not rely on it as the only method if the tyre looks close to the legal limit.

When Should Tyres Be Replaced?

Tyres should be replaced immediately if they are below the legal tread depth, visibly damaged or unsafe.

Drivers should also consider replacing tyres before they reach the legal minimum, especially if they regularly drive in heavy rain, on motorways or during winter conditions.

What Are the Legal Requirements for Brakes?

Brakes must be kept in proper working condition because they are essential for stopping safely.

The MOT checks the condition, operation and performance of the braking system. It also checks warning lights linked to systems such as ABS, ESC, electronic parking brake and brake fluid where fitted.

Warning signs of brake problems include:

• Grinding or squealing noises
• A soft or spongy brake pedal
• The car pulling to one side when braking
• Vibration through the brake pedal
• Longer stopping distances
• Brake warning light staying on
• Burning smell after braking

Drivers should not continue using a vehicle if they suspect a serious brake fault. A car with dangerous brake defects may be treated as unroadworthy.

What Are the Legal Requirements for Steering?

The steering system must allow the driver to control the vehicle safely. If steering becomes loose, stiff, delayed or unpredictable, the vehicle may be unsafe.

Common signs of steering problems include:

• Steering wheel vibration
• Car drifting to one side
• Excessive play in the steering wheel
• Difficulty turning
• Unusual knocking or whining sounds
• Uneven tyre wear
• Warning lights related to power steering

Steering defects should be checked quickly because they can affect emergency handling, cornering and control at speed.

What Are the Legal Requirements for Lights and Indicators?

A car’s lights and indicators must work correctly because they help the driver see and allow other road users to understand what the vehicle is doing.

Important lights include:

• Headlights
• Brake lights
• Rear lights
• Indicators
• Hazard warning lights
• Fog lights
• Reversing lights, where fitted
• Number plate lights

The Road Vehicles Lighting Regulations cover the maintenance and use of vehicle lighting, and MOT checks include lighting condition, operation and aim.

A faulty brake light or indicator may seem minor, but it can create danger because other drivers may not know when the vehicle is stopping or turning.

What Are the Legal Requirements for the Windscreen?

The windscreen must give the driver a clear view of the road. Cracks, chips, heavy dirt, stickers or hanging items can become a problem if they obstruct the driver’s view.

The MOT checks the windscreen’s condition and the driver’s view of the road. It also checks whether wipers and washers work properly.

Drivers should take action if:

• A crack or chip is in the driver’s line of sight
• Wipers leave heavy smears
• Washer jets do not work
• Washer fluid is empty
• The windscreen is heavily dirty or iced over
• Items hanging from the mirror block the view

A clean windscreen is a simple legal and safety requirement that many drivers overlook.

What Are the Legal Requirements for Wipers and Washers?

Wipers and washers must work well enough to keep the windscreen clear. If the wipers are split, noisy, stiff or leave large smears, they may not be doing their job properly.

Washer fluid should also be topped up. Driving without enough washer fluid can become dangerous if dirt, salt, insects or spray from other vehicles blocks the driver’s view.

Drivers should replace wiper blades when they:

• Smear water
• Leave streaks
• Miss parts of the windscreen
• Make loud scraping noises
• Have visible splits or hardened rubber

What Are the Legal Requirements for Mirrors?

Mirrors are needed so the driver can see behind and around the vehicle. Missing, cracked or badly adjusted mirrors can reduce awareness when changing lanes, turning, reversing or joining traffic.

Drivers should make sure:

• Mirrors are present where required
• Mirror glass is not cracked or missing
• Mirrors are secure
• Electric adjustment works where needed
• The driver has a clear rear and side view

A damaged mirror should be repaired quickly, especially if it affects visibility on the driver’s side.

What Are the Legal Requirements for Seat Belts?

Seat belts must be secure, functional and in good condition where they are required.

The MOT checks that mandatory seat belts are present, suitable, in good condition, working correctly and securely attached.

Seat belt faults include:

• Frayed webbing
• Cuts or tears
• Faulty buckle
• Poor retraction
• Damaged mounting points
• Warning system faults where tested

Drivers should not ignore damaged seat belts because they are a major passenger safety system.

What Are the Legal Requirements for Suspension?

Suspension helps keep the vehicle stable and keeps the tyres in proper contact with the road. Worn or broken suspension can affect steering, braking and handling.

Signs of suspension problems include:

• Knocking noises over bumps
• Uneven tyre wear
• Vehicle leaning to one side
• Poor handling
• Bouncing after going over bumps
• Longer stopping distances
• Steering instability

The MOT includes suspension checks because suspension faults can affect road safety.

What Are the Legal Requirements for Exhaust and Emissions?

The exhaust system must be secure, leak-free and not excessively noisy. The vehicle must also meet required emissions standards during MOT testing.

A faulty exhaust can cause:

• Excessive noise
• Smoke
• Exhaust fumes entering the cabin
• MOT failure
• Higher emissions
• Reduced fuel efficiency

Drivers should also avoid removing or tampering with emissions control equipment, such as catalytic converters or diesel particulate filters, because this can create MOT and legal problems.

What Are the Legal Requirements for Number Plates?

Number plates must clearly display the vehicle registration number. GOV.UK states that drivers must not rearrange letters or numbers or alter them so they become hard to read.

Incorrectly displayed number plates can lead to a fine of up to £1,000 and MOT failure.

Number plates should be:

• Clean
• Easy to read
• Properly spaced
• Securely attached
• Correct size and colour
• Not cracked or damaged
• Not covered by dirt, film or tinted covers
• Not altered to misrepresent characters

This is important because registration plates help police, DVLA, parking authorities and automatic number plate recognition systems identify vehicles.

Does Passing an MOT Mean the Car Is Legal for the Whole Year?

No. Passing an MOT does not mean the car is guaranteed to be legal for the whole year.

GOV.UK states that a vehicle can be unsafe even if it has a current MOT certificate. Drivers remain responsible for making sure the vehicle is roadworthy whenever it is used.

The MOT checks whether important parts meet minimum legal standards at the time of the test.

GOV.UK also explains that an MOT is not the same as having the vehicle serviced and does not check the general mechanical condition of the engine, clutch or gearbox.

A car can become illegal after passing an MOT if:

• A tyre becomes worn below the legal limit
• A brake light fails
• A windscreen crack spreads
• A seat belt stops latching
• Brake performance worsens
• Steering develops a dangerous fault
• A number plate becomes unreadable
• Suspension components fail

What Car Defects Can Lead to Fines or Penalty Points?

Defects that affect safety or legality can lead to penalties. The most serious defects include:

• Illegal tyres
• Faulty brakes
• Dangerous steering faults
• Defective lights
• Unsafe suspension
• Obstructed windscreen view
• Unreadable number plates
• Excessive smoke or emissions
• Dangerous structural faults

The penalty depends on the defect and the circumstances. GOV.UK confirms that driving a vehicle in a dangerous condition can lead to a fine of up to £2,500, a driving ban and 3 penalty points.

What Happens If Your Car Fails an MOT?

If a car fails its MOT, the next steps depend on the type of defect.

MOT defects can be classed as:

• Dangerous
• Major
• Minor
• Advisory

GOV.UK states that drivers can be fined up to £2,500, banned from driving and given 3 penalty points for driving a vehicle that has failed its MOT because of a dangerous problem before it has been repaired.

A dangerous defect means the vehicle should not be driven until repaired. A major defect means the vehicle has failed the MOT and needs repair.

Minor defects should be fixed as soon as possible, while advisory items should be monitored because they may become more serious.

Can Your Insurance Be Affected If the Car Is Not Roadworthy?

Yes, poor vehicle maintenance can create insurance problems, especially if a defect contributed to an accident.

For example, if a vehicle had illegal tyres, faulty brakes or broken lights at the time of a collision, the insurer may investigate whether the car was being kept in a safe and roadworthy condition.

Insurance policy wording can vary, so drivers should check their own policy documents. However, the safest approach is to keep the car roadworthy, repair safety defects quickly and keep service or repair records.

What Should Drivers Check Before Every Journey?

Drivers should carry out basic checks before driving, especially before long journeys, motorway trips or bad-weather driving.

Before setting off, check:

• Windscreen is clear
• Mirrors are clean and correctly adjusted
• Lights and indicators work
• Tyres do not look flat or damaged
• Number plates are readable
• Brakes feel normal
• No warning lights stay on
• Washer fluid is available
• Wipers clear the screen properly

GOV.UK advises drivers to check that the windscreen, windows and mirrors are clean, that all lights work and that the brakes work every time they drive.

Monthly Car Roadworthiness Checklist

Drivers should also complete a more detailed check at least once a month.

Check	What to Look For
Tyres	Tread depth, pressure, cuts, bulges, uneven wear
Lights	Headlights, brake lights, indicators, fog lights
Brakes	No unusual noise, vibration or delayed response
Wipers	No smearing, splitting or poor contact
Washer fluid	Fluid topped up and jets working
Windscreen	No serious chips, cracks or blocked view
Mirrors	Secure, clean and properly adjusted
Number plates	Clean, readable and correctly displayed
Seat belts	Latch, retract and show no damage
Fluids	Oil, coolant, brake fluid, washer fluid
Warning lights	Investigate any lights that remain on
Suspension	Listen for knocking or unstable handling

What Are the Most Common MOT Failures Linked to Poor Maintenance?

Many MOT failures are caused by simple maintenance issues that could have been spotted earlier.

Common failure areas include:

• Lights and signalling
• Suspension
• Brakes
• Tyres
• Driver’s view of the road
• Emissions
• Seat belts
• Registration plates

GOV.UK’s MOT guidance confirms that many of these systems are checked during the MOT, including lamps, brakes, tyres, seat belts, registration plates, steering, suspension, emissions, wipers and washers.

What Should You Do If You Find a Defect?

If you find a defect, the safest response depends on how serious it is.

Do not drive the car if:

• Brakes feel unsafe
• Steering is not working properly
• Tyres are illegal or damaged
• Warning lights suggest a serious fault
• The windscreen view is seriously blocked
• Seat belts do not work
• Suspension feels unstable
• The vehicle is producing heavy smoke or fumes

Arrange repair quickly if:

• A light bulb has failed
• Wipers are smearing
• Washer fluid is empty
• Number plates are dirty or damaged
• Tyres are close to the legal limit
• A minor chip appears in the windscreen
• A mirror is cracked but still usable

If there is any doubt, drivers should ask a qualified mechanic, MOT tester or garage to inspect the vehicle.

Who Is Responsible for Keeping the Car Legal?

The driver is responsible for making sure the vehicle is safe before using it. The registered keeper may also have responsibilities, especially if they allow someone else to use a vehicle that is unsafe.

A garage or MOT centre can inspect, service and repair the vehicle, but the driver still needs to make sure it is safe before driving.

For company cars, fleet vehicles, taxis, vans and commercial vehicles, the legal responsibilities may be stricter and may involve employers, operators or licence holders as well as drivers.

Common Myths About Car Roadworthiness Law

Myth 1: “A valid MOT means the car is legal for 12 months.”

This is false. GOV.UK says a vehicle can be unsafe even if it has a current MOT certificate.

Myth 2: “Only tyres and brakes matter.”

This is false. Tyres and brakes are very important, but the law also covers lights, mirrors, steering, suspension, seat belts, visibility, exhaust systems and number plates.

Myth 3: “Small defects are not serious.”

Small defects can become serious quickly. A worn tyre, faulty brake light, cracked mirror or poor wiper blade can affect safety and legality.

Myth 4: “An MOT is the same as a service.”

This is false. GOV.UK confirms that an MOT is not the same as servicing and does not check the general mechanical condition of the engine, clutch or gearbox.

Myth 5: “Insurance always pays out even if the car is unsafe.”

Not always. If poor maintenance contributed to an accident, the insurer may investigate the condition of the vehicle and the driver’s compliance with policy terms.

Practical Example: Is the Car Still Legal?

Here are some common examples.

Situation	Possible Legal Risk
One brake light has failed	May lead to MOT failure or roadside action
Tyre tread is below 1.6mm	Illegal and may lead to fine and points
Windscreen washer fluid is empty	May affect visibility and MOT outcome
Number plate is dirty and unreadable	Can lead to fine and MOT failure
Car passed MOT last month but brakes now grind	Vehicle may be unsafe despite valid MOT
Mirror is cracked and visibility is poor	May affect roadworthiness
Wipers smear heavily in rain	May affect driver’s view and safety

Conclusion

UK law requires drivers to keep the whole car in a safe and roadworthy condition, not just one part.

The most important parts include tyres, brakes, steering, lights, mirrors, windscreen, wipers, washers, seat belts, suspension, exhaust system, emissions equipment and number plates.

A valid MOT certificate does not remove the driver’s responsibility. The vehicle must be safe every time it is driven.

Regular checks, prompt repairs and professional servicing help drivers avoid fines, penalty points, MOT failure, insurance problems and preventable accidents.

For most drivers, the best rule is simple: if a defect affects braking, steering, visibility, tyres, lights, seat belts or identification, treat it as urgent.

FAQs

What part of the car does the law require you to keep in good condition?

UK law requires the whole vehicle to be kept roadworthy. Important parts include tyres, brakes, steering, lights, mirrors, windscreen, wipers, washers, seat belts, suspension, exhaust system and number plates.

Is it illegal to drive with worn tyres in the UK?

Yes. Cars, light vans and light trailers must have at least 1.6mm tread depth across the central three-quarters of the tread and around the full circumference.

What is the fine for illegal tyres in the UK?

Drivers stopped with illegal tyres could receive a £2,500 fine and 3 penalty points per tyre.

Does an MOT mean my car is roadworthy for the full year?

No. GOV.UK says a vehicle can be unsafe even if it has a current MOT certificate. Drivers are responsible for keeping the vehicle safe whenever it is used.

Can I drive a car after it fails an MOT?

It depends on the defect. If the MOT failure includes a dangerous defect, GOV.UK says you can be fined up to £2,500, banned from driving and given 3 penalty points for driving it before repair.

Can a dirty number plate lead to a fine?

Yes. GOV.UK states that incorrectly displayed number plates can lead to a fine of up to £1,000 and MOT failure.

Are faulty lights illegal?

Faulty lights can make a vehicle unsafe and may lead to MOT failure or enforcement action. MOT checks include lamps, reflectors, indicators, brake lights and headlamp aim.

Is a cracked windscreen illegal?

A cracked windscreen can become illegal or cause MOT failure if it affects the driver’s view of the road or compromises safety. The MOT checks windscreen condition and driver visibility.

Are wipers and washers checked in an MOT?

Yes. The MOT checks whether wipers and washers work properly so the driver has a clear view of the road.

Can poor car maintenance affect insurance?

Yes. If an accident involves a vehicle defect, such as illegal tyres or faulty brakes, the insurer may investigate whether the car was being kept roadworthy. Drivers should check their policy wording and keep safety defects repaired.

How often should I check my car?

Drivers should check basic safety items before driving and carry out more detailed checks monthly. GOV.UK advises drivers to check the windscreen, windows, mirrors, lights and brakes every time they drive.

Who is responsible if a car is unroadworthy?

The driver is responsible for making sure the vehicle is safe before driving. A registered keeper, employer or operator may also have responsibilities depending on who owns, controls or allows use of the vehicle.

What are the most important car safety checks before a long journey?

Before a long journey, check tyres, tyre pressure, lights, indicators, brakes, oil, coolant, washer fluid, wipers, mirrors, windscreen and number plates.

What does roadworthy mean?

Roadworthy means the vehicle is safe and legal to use on public roads. It should not have defects that create danger, reduce control, block visibility, prevent identification or breach vehicle safety rules.

What car defects are most likely to be serious?

Tyre defects, brake faults, steering problems, suspension failure, broken lights, poor visibility, seat belt defects and dangerous exhaust faults are among the most serious because they directly affect safety.

Editorial Note

This article is based on official UK road safety, MOT, vehicle maintenance and legislation guidance. It is intended for general information only and should not be treated as legal advice.

Drivers with specific concerns about prosecution, insurance disputes or vehicle defects should speak to a qualified motoring solicitor, insurer, MOT tester or professional mechanic.

Sources and References

This guide was prepared using official UK government and road safety sources, including:

• GOV.UK guidance on checking whether a vehicle is safe to drive
• The Highway Code guidance on vehicle maintenance, safety and security
• GOV.UK guidance on car parts checked during an MOT
• GOV.UK guidance on MOT test results and dangerous defects
• GOV.UK rules on displaying number plates
• Road Traffic Act 1988, Section 40A on using a vehicle in a dangerous condition
• Road Vehicles Construction and Use Regulations 1986, Regulation 100
• Road Vehicles Lighting Regulations 1989
• THINK! road safety guidance on vehicle safety checks
• nidirect vehicle maintenance, safety and security guidance