The law on a car's condition: Great Britain and Northern Ireland

Picture two defects found at the same roadside check after dark: a tyre worn below the legal depth and a number-plate lamp that doesn't light. Most drivers would call both "illegal" and stop there. The law in Great Britain doesn't. One of them falls under a section of the Road Traffic Act 1988 that carries three penalty points on your licence; the other, on this course's reading, falls under a later section that carries none. And an MOT pass last month changes neither, because the duty the law puts on a driver runs every time the car is used. This lesson reads that law in its own words, so you can say which rule a defect breaks, what can follow, who it reaches, and where the law in Northern Ireland is written instead.

Most of this lesson is law, so here is the full caution once; each section after this opens with the short form. This is general information, not legal advice. The rules differ between England and Wales, Scotland, Northern Ireland and each US state, and they change. This lesson doesn't tell you what applies in your own case. It tells you which rule a set of facts points to, in the rule's own words, and whom to ask.

Where the law comes from, in Great Britain

This is general information, not legal advice.

Earlier lessons met the rules one at a time: the tread and tyre rules in regulation 27 (lessons 8 and 18), glass, wipers and washers in regulations 30 and 34 (lessons 9 and 10), lamps in regulation 23 of the Lighting Regulations (lesson 10), and a removed diesel particulate filter in regulation 61A (lesson 3). Those lessons are lesson 3, "Diesel exhaust: the DPF and AdBlue"; lesson 8, "Tyres II: tread, damage, age, and when to replace"; lesson 9, "Under the bonnet: oil, coolant, brake fluid and screenwash"; lesson 10, "Lights, wipers, glass and the walk-round"; and lesson 18, "A flat tyre: the decision, and spare, space saver, sealant or run-flat". The rules sit in three layers, and it helps to see them together.

The statute. The Road Traffic Act 1988 creates the offences. Its sections 40A, 41A and 42 are the ones about a car's condition, and each applies in England, Wales and Scotland.¹²³

The regulations. Section 41 of the Act lets the government make regulations "as to the use of motor vehicles and trailers on roads, their construction and equipment", and it defines "construction and use requirements" as requirements "imposed under this section".⁴ The Road Vehicles (Construction and Use) Regulations 1986 are the main set of those regulations. They were made under the Road Traffic Act 1972, which the 1988 Act replaced, and this course reads them as carried over; it didn't read the provision that does that.²⁴ The Road Vehicles Lighting Regulations 1989 say on their face that they were made under "section 41 as read with section 43" of the 1988 Act.⁴ So a regulation like 27 sets the standard, and the Act makes breaking it an offence.

The Highway Code. It restates the law and adds advice, and lesson 1, "What a car is made of, and why the handbook comes first", taught its two voices. Rules that are law "are identified by the use of the words 'MUST/MUST NOT'", and, the introduction adds, "In addition, the rule includes an abbreviated reference to the legislation which creates the offence."⁵ Rule 89 is the one that covers this whole lesson in a line: "Vehicle condition. You MUST ensure your vehicle and trailer comply with the full requirements of the Road Vehicles (Construction and Use) Regulations and Road Vehicles Lighting Regulations".⁶ The Code does not create that duty. It points to the regulations that do.

Rule 97 shows both voices in one place. Before setting off, "You MUST ensure that" your licence and insurance are valid and "your vehicle is legal and roadworthy"; then, under "You SHOULD ensure that", comes "you have sufficient fuel or charge for your journey, especially if it includes motorway driving".⁶ The first half is law. The second is advice that, the introduction says, "may be used in evidence in any court proceedings under the Traffic Acts".⁵

Lesson 11, "Dashboard warning lights", met another advice line: Annex 6 says that if the warning lights stay on after the engine starts, "stop and investigate the problem, as you could have a serious fault."²⁵ It has no MUST, so a driver who ignores it breaks nothing in the Code's words. The fault behind the light is another matter. If it breaks a construction and use requirement, Rule 89's MUST points to it, and the offence is in the Act, whatever the dashboard showed.

Three offences, and why only some carry points

This is general information, not legal advice.

Section 40A: a dangerous condition

Section 40A begins: "A person is guilty of an offence if he uses, or causes or permits another to use, a motor vehicle or trailer on a road when". Four things follow, and the first is "the condition of the motor vehicle or trailer, or of its accessories or equipment". The other three are the purpose it's used for, its passengers, and its load. The offence is made out when any of them "is such that the use of the motor vehicle or trailer involves a danger of injury to any person."¹

Notice that it names no part. It asks whether using the car, in the state it's in, involves a danger of injury to anyone.

Section 41A: brakes, steering-gear or tyres

Section 41A is narrower. A person commits it who "contravenes or fails to comply with a construction and use requirement as to brakes, steering-gear or tyres", or who "uses on a road a motor vehicle or trailer which does not comply with such a requirement, or causes or permits a motor vehicle or trailer to be so used".² No danger has to be shown. A tyre that breaks regulation 27 is enough.

Section 42: everything else in the regulations

Section 42 is headed "Breach of other construction and use requirements". It reaches any construction or use requirement other than the brakes, steering-gear and tyres ones in section 41A and two others (weight limits for goods and passenger vehicles, in section 41B, and the driver's control and view of the road and hand-held phones, in section 41D), in the same two ways: breaking the requirement, or using, causing or permitting the use of a vehicle that breaks it.³⁷ Lamps, glass, wipers, washers and avoidable smoke are requirements of this kind. That a lamp falls here is this course's reading of the words, from section 42 and the Lighting Regulations' own statement that they were made under section 41. So, on this course's reading, is regulation 61A's rule against using a car whose emissions fail their limits because the exhaust was altered (lesson 3's removed filter); the £1,000 for a car in the DVSA note lesson 3 quoted is the level 3 figure in the table below.

What each one carries

The penalties aren't in those sections. They're in Schedule 2 of the Road Traffic Offenders Act 1988, a long table with one row per offence, which this course read for these rows.⁷ It gives each maximum as a "level on the standard scale", and the Sentencing Act 2020, section 122, converts the levels into pounds for England and Wales: for an offence committed on or after 1 October 1992, level 3 is £1,000 and level 4 is £2,500.⁸ Scotland has its own standard scale, which this course didn't read, so the pound figures below are England and Wales's.

Sources: Road Traffic Offenders Act 1988, Schedule 2, Part I; Sentencing Act 2020, s.122; all read on the live pages on 26 September 2026.⁷⁸ Goods vehicles and vehicles adapted to carry more than eight passengers have a higher level in each row.

Three words in that table. A ban is disqualification from driving. Endorsement means the offence goes on the driver's record with its points, as lesson 8 put it. Schedule 2's own words are "obligatory", which the table gives as must, and "discretionary", given as may.

DVLA (the Driver and Vehicle Licensing Agency) has its own codes. On this course's reading of their descriptions, CU20 (unsuitable vehicle, or parts or accessories other than brakes, steering or tyres) and CU50 (load or passengers) go with section 40A, and CU10 (brakes), CU30 (tyres) and CU40 (steering) with section 41A. DVLA's page doesn't name the sections, and because CU20's description leaves out brakes, steering and tyres, this course cannot say which code a section 40A conviction about those parts would get. The page says construction and use codes "must stay on a driving record for 4 years from the date of the offence."⁹

GOV.UK puts the first row in plain words: "You can be fined up to £2,500, be banned from driving and get 3 penalty points for driving a vehicle in a dangerous condition."¹⁰

Regulation 100, the "at all times" rule

One regulation states the idea of section 40A as a standing duty. Regulation 100 of the Construction and Use Regulations is headed "Maintenance and use of vehicle so as not to be a danger, etc", and its first paragraph says: "A motor vehicle, every trailer drawn thereby and all parts and accessories of such vehicle and trailer shall at all times be in such condition". The sentence goes on to passengers and loads, and ends: "that no danger is caused or is likely to be caused to any person in or on the vehicle or trailer or on a road."¹¹ "At all times" is the phrase to hold on to. It does not wait for a test date. Which section a breach of regulation 100 is charged under is not something this course read about, so the lesson goes no further than its words.

Regulation 27, the whole of it

Lesson 18, "A flat tyre: the decision, and spare, space saver, sealant or run-flat", promised this lesson would come back to regulation 27 as a whole. Its paragraph (1) says a vehicle with pneumatic tyres "shall not be used on a road, if" any of a list is true, and for a car the list comes down to this:¹²

• (a) the tyre is unsuitable for the use, or for the tyres on the other wheels;
• (b) it's not inflated fit for the use (lesson 7, "Tyres I: pressure, the placard and TPMS");
• (c) to (e) a cut over 25 mm or 10% of the section width, whichever is the greater, that reaches the ply or cord, a lump, bulge or tear from structural failure, or ply or cord exposed (lesson 8);
• (h) "the tyre is not maintained in such condition as to be fit for the use to which the vehicle or trailer is being put", or has a defect that might damage the road or people.

Paragraph (2) lets a tyre that is built and marked to run deflated (a run-flat) be used that way; paragraph (3) keeps a space saver out of (a)'s "unsuitable" rule only while the car isn't driven over 50 mph (lesson 18); and paragraph (4)(f) sets the car tread rule, 1.6 mm "throughout a continuous band comprising the central three-quarters of the breadth of tread and round the entire outer circumference of the tyre" (lesson 8).¹² The ten-year age limits in paragraphs (1)(i) and (j), and the illegible-date rule in (1)(k), apply only to buses, minibuses and heavier goods vehicles, not to cars. On this course's reading, every one of these is a requirement "as to tyres", so a breach falls under section 41A.

A roadside check near Spalding

This is general information, not legal advice.

On a wet night near Spalding, police stop a car at a roadside check. One front tyre's grooves measure under 1.6 mm across the middle of the tread, all the way round. One of the car's two stop lamps is out. Nothing else is wrong. Three questions: which section of the Act does each defect point to, which carries points, and what does the Sentencing Council's guideline for England and Wales add about the tyre?

The tyre first. It breaks regulation 27(4)(f), a construction and use requirement as to tyres, so it points to section 41A: a £2,500 maximum, obligatory endorsement and 3 points (on this course's reading of DVLA's list, code CU30).²⁷⁹ The Sentencing Council's guideline, "Tyres defective", is for magistrates in England and Wales. It gives "Maximum for vehicles up to 3.5 tonnes: Level 4 fine", "Must endorse and impose 3 points", a starting point of a "Band B fine" for a driver, which the guideline sets at 100% of relevant weekly income, and then the line lesson 8 quoted: "Fine is for each single tyre (but ordinarily only one set of points apply where several offences committed on the same occasion)."¹³ One tyre here, so one fine. The guidelines for brakes and for steering, which this course also read, give the same maximum and the same "Must endorse and impose 3 points".¹³

Now the lamp. Your turn before the answer: which section, and does it carry points?

Section 40A could come into it as well, if the facts showed that using the car involved a danger of injury. Whether they do is a question of fact, and which offence gets charged is a prosecutor's decision. This course can only say which words each set of facts meets.

Did not know, and had no reasonable cause to suspect

This is general information, not legal advice.

Lesson 8, "Tyres II: tread, damage, age, and when to replace", quoted one half of this rule. Here is all of it. Section 48 of the Road Traffic Offenders Act 1988 has two subsections. Each says that, on conviction, the court must not order disqualification or order the offence's details (its "particulars") or penalty points to be endorsed on the driving record, and each sets its own condition. For section 40A it is "if he proves that he did not know, and had no reasonable cause to suspect, that the use of the vehicle involved a danger of injury to any person." For section 41A it is "if he proves that he did not know, and had no reasonable cause to suspect, that the facts of the case were such that the offence would be committed."¹⁴

Three things follow from the words, and the first two are easy to miss.

It removes the points and the ban. It doesn't remove the conviction or the fine. The section's own heading calls it an "Exemption from disqualification and endorsement", the word lesson 8 used. It is not a defence to the offence itself, and calling it a loophole gets it wrong.¹⁴

"If he proves." The burden in those words is on the person convicted, not on the prosecution.

"No reasonable cause to suspect" is wider than "didn't know". On this course's reading, a defect that a look would have shown gave cause to suspect whether or not anybody looked. On that reading, the checks in lessons 7 to 10 carry legal weight in Great Britain: they're how a driver finds the defect first, and a driver who never looks is in a weaker position under section 48, not a stronger one. Section 48 has no subsection for section 42, and section 42 carries no points to remove.

Who the law reaches: uses, causes or permits

This is general information, not legal advice.

All three sections reach more than the driver. Each covers a person who "uses" the vehicle and a person who "causes or permits" it to be used.¹²³ This course reads those words as they stand and does not interpret them further; it read no case law on what "permits" requires. What it can do is show which words a set of facts turns on.

A lent car in Corby

An owner in Corby lends her car to a friend for the weekend. On Saturday the friend drives it to a supermarket with a bulge in the outer sidewall of a rear tyre. The bulge is a breach of regulation 27(1)(d), a requirement as to tyres.

Start with the section: it's 41A. Now the gap. Before you read the answer, say which words of section 41A reach each of them, and which words of section 48(2) the question for each then turns on. Answer as "which rule, and what it asks", not "is she guilty".

A few practical lines follow, and all are this course's reading, not something a statute says. If you lend a car, the tyres and lights are worth a look before the keys change hands, because the words reach you. If you borrow one, the walk-round in lesson 10 is quick, and it comes before you drive. And if the car belongs to a lease, finance or hire company, or an employer, the agreement decides who arranges tyres and repairs; this course read none of those agreements, so tell the company in writing and do only the owner's checks.

What else the law asks of a driver in Great Britain

This is general information, not legal advice.

A car's condition is one of several things the law asks for before it's driven. GOV.UK's page "Legal obligations of drivers and riders" lists them: the vehicle must "be registered with DVLA", "have up to date vehicle tax", "have a current MOT certificate (if your vehicle needs one)" and "be roadworthy", and "You must also have a minimum of third party insurance that covers your use of the vehicle."¹⁵ If a police officer asks, you must be able to show your licence, "a valid insurance certificate" and "a valid MOT certificate (if your vehicle needs one)", and if they're not with you, "you may be asked to take them to a police station within 7 days."¹⁵

Two of those link back to condition. The MOT is the subject of lesson 21, "The MOT and Northern Ireland's vehicle test"; the offence of using a car with no current test certificate is section 47 of the Act, and Schedule 2 gives it "Level 3 on the standard scale in any other case" than larger passenger vehicles, with no endorsement and no points.⁷ And insurance: the Highway Code's Annex 3 says "Driving an unroadworthy motor vehicle may invalidate your insurance."¹⁶ Keep the "may". Insurance itself belongs to Personal Finance Fundamentals lesson 8, "Handing off what you cannot absorb".

The Code's Annex 5, on penalties, has a table that gives "Using a vehicle in a dangerous condition" a £2,500 maximum for a car and "3 in each case", and "No MOT certificate" a £1,000 fine and no points.¹⁷ Those match the statute's rows above.

Northern Ireland: its own law, in almost the same words

This is general information, not legal advice.

Every section of the Road Traffic Act and the Offenders Act above extends to England, Wales and Scotland and stops there, and so do the regulations. Northern Ireland, as nidirect puts it, "is largely responsible for its own road safety policy and legislation".¹⁸ Earlier lessons said this course hadn't read that legislation. For this lesson it read the parts that match the ones above, and they're close to word for word.

The offences. Northern Ireland's Road Traffic (Northern Ireland) Order 1995 has its own three articles. An Order is a kind of statutory instrument (this one is SI 1995/2994), not an Act, and where an Act has sections, an Order has Articles. Article 54, "Using vehicle in dangerous condition etc.", opens with the same words as section 40A: "A person is guilty of an offence if he uses, or causes or permits another to use, a motor vehicle or trailer on a road when".¹⁹ Article 56 makes it an offence to contravene "a construction and use requirement as to brakes, steering-gear or tyres", or to use, cause or permit the use of a vehicle that doesn't comply.¹⁹ Article 58 covers the other requirements.¹⁹

The regulations. Northern Ireland has its own Motor Vehicles (Construction and Use) Regulations (Northern Ireland) 1999. Its regulation 32 sets the same car tread rule, 1.6 mm "throughout a continuous band comprising the central three-quarters of the breadth of tread and round the entire outer circumference of the tyre", and its regulation 115 is the "Maintenance and use of vehicle so as not to be a danger" rule.²⁰ One caution: legislation.gov.uk carries these regulations only as made in 1999, with no revised version, so this course read the original text and not any later amendment.

The Highway Code. Northern Ireland's own Code, on nidirect, uses the same two voices, and its legal rules "are identified by the use of the words ‘must’ and ‘must not’", in lower case.¹⁸ Its annex on vehicle maintenance gives the car tread rule as a must, "Must have a tread depth of at least 1.6 mm across the central three-quarters of the breadth of the tread and around the entire circumference", citing "CUR reg 32".²¹

Advice. nidirect's page "Maintaining your vehicle" lists weekly checks, including that "there must be at least the legal minimum 1.6 mm of tread and preferably more than 2 mm".²² The 1.6 mm is the law; "preferably more than 2 mm" is nidirect's advice, and lesson 8 set out the argument about margins above the floor.

What wasn't read. The penalties Northern Ireland attaches to Articles 54, 56 and 58; whether it has a rule like section 48; and its scale of fines. nidirect's fixed-penalty page, which says "A Fixed Penalty is a fine for a motoring offence", gives one example that bears on this lesson: the Driver and Vehicle Agency's fixed penalty notices can be "endorsable - for example, for a defective tyre", with no figure.²³ Northern Ireland's Highway Code penalty table, as read, has no row for a car's condition.²¹ And DVLA's page, which is Great Britain's, says: "Endorsement codes and processes in Northern Ireland are different."⁹

What people get wrong

This is general information, not legal advice.

"It passed its MOT, so it's legal." Lesson 1 quoted GOV.UK on this: a current certificate doesn't make a car roadworthy. The three offences above apply every time the car is used, and lesson 21 covers what the test does.

"Three points for every bad tyre." The Spalding section has the guideline's words on fines and points.

"'Didn't know' gets you off." "Did not know, and had no reasonable cause to suspect", above, has section 48's words and what they leave in place.

"No MOT means points." Not on the Schedule 2 row this course read; "What else the law asks of a driver in Great Britain" has it, and lesson 21 has the government's consultation.

"The Highway Code is only advice." "Where the law comes from, in Great Britain" has its two voices, with Rule 97 as the example.

"Northern Ireland follows the same law." The Northern Ireland section above has what this course read and didn't; a reader there checks nidirect.

Practice

For your plan

Add a legal page to your car file, after the wheel page from lesson 19, "Changing a wheel safely". On it: which country's law applies to the roads you drive (Great Britain or Northern Ireland; lesson 22, "The US: state inspections, emissions tests and tread law", covers the US states), the three offences in one line each with their points, section 48's two conditions in its own words, and a line pointing to the checks log you started in lesson 10, since, on this course's reading, a dated record like that is the kind of thing that bears on "no reasonable cause to suspect".

Connections

Lesson 1 taught the Highway Code's two voices, and that the driver, not the test, answers for the car's condition; this lesson traced both to the statute. Lessons 3, 7, 8, 9, 10 and 18 each taught a regulation, and this lesson showed which section of the Act each one hangs from. Home Repair and Maintenance lesson 22, "Who may do what: reserved work, and the argument about licensing", showed the same shape in building work, with separate rules for England, Wales, Scotland and Northern Ireland. Lesson 21 takes the test itself, and lesson 22 the US.

Go deeper

• Road Traffic Act 1988, sections 40A to 42, free on legislation.gov.uk. Read here in full. Three short sections, and worth reading in their own words rather than as advice pages repeat them.
• Road Traffic Offenders Act 1988, section 48, free. Read here in full. Two subsections; the "if he proves" is the part people miss.
• Sentencing Council, "Tyres defective", free, England and Wales. Read here in full, with the brakes and steering guidelines. What a magistrates' court starts from.
• nidirect, "Vehicle maintenance, safety and security", free. Read here in full. Northern Ireland's own Highway Code annex, with the laws it cites.

Sources

1. Road Traffic Act 1988, section 40A, latest revised text. England, Wales and Scotland. Read: the whole section on the live page, 26 September 2026.
2. Road Traffic Act 1988, section 41A, as above. Read: the whole section, 26 September 2026.
3. Road Traffic Act 1988, section 42, as above. Read: the whole section, 26 September 2026.
4. Road Traffic Act 1988, section 41, and the Road Vehicles Lighting Regulations 1989, introduction. Read: section 41 in full, and the Lighting Regulations' opening words on the powers used, 26 September 2026.
5. The Highway Code, "Introduction", updated 1 July 2022. Great Britain. Read: full text through the GOV.UK content API, 26 September 2026.
6. The Highway Code, "Rules for drivers and motorcyclists (89 to 102)", updated 14 September 2021. Great Britain. Read: Rules 89 to 98 in full, 26 September 2026.
7. Road Traffic Offenders Act 1988, Schedule 2, Part I, latest revised text. England, Wales and Scotland. Read: the rows for Road Traffic Act sections 40A, 41A, 41B, 41D, 42 and 47, and the column headings, 26 September 2026.
8. Sentencing Act 2020, section 122. England and Wales. Read: the whole section, 26 September 2026. Scotland's standard scale was not read.
9. GOV.UK (DVLA), "Penalty points (endorsements)", updated 27 January 2025. Great Britain. Read: full guide through the content API, 26 September 2026.
10. GOV.UK (DVSA), "Check your vehicle is safe to drive", updated 5 April 2018. Read: full text, re-read 26 September 2026.
11. Road Vehicles (Construction and Use) Regulations 1986, regulation 100, as amended. England, Wales and Scotland. Read: the whole regulation, 26 September 2026.
12. Road Vehicles (Construction and Use) Regulations 1986, regulation 27, as amended. England, Wales and Scotland. Read: the whole regulation, 26 September 2026.
13. Sentencing Council, "Tyres defective", "Brakes defective" and "Steering defective", magistrates' guidelines effective from 4 August 2008. England and Wales. Read: the tyres guideline in full; the brakes and steering guidelines' offence, maximum, endorsement and starting-point lines, 26 September 2026.
14. Road Traffic Offenders Act 1988, section 48, latest revised text. England, Wales and Scotland. Read: the whole section, 26 September 2026.
15. GOV.UK, "Legal obligations of drivers and riders", updated 27 August 2015. Read: full text, 26 September 2026.
16. The Highway Code, "Annex 3. Motor vehicle documentation and learner driver requirements", updated 20 May 2018. Great Britain. Read: full text, 26 September 2026.
17. The Highway Code, "Annex 5. Penalties", updated 27 July 2022. Great Britain. Read: full text, 26 September 2026.
18. nidirect, "Introduction to the Highway Code", Northern Ireland, modified 22 September 2026. Read: full text, 26 September 2026.
19. Road Traffic (Northern Ireland) Order 1995, Articles 54, 56 and 58 (SI 1995/2994), latest revised text. Northern Ireland. Read: the three articles in full, and the Order's introductory text, 26 September 2026. Nothing else in the Order was read for this lesson.
20. Motor Vehicles (Construction and Use) Regulations (Northern Ireland) 1999, regulations 32 and 115 (SR 1999/454), as made; legislation.gov.uk has no revised version. Read: both regulations as made, 26 September 2026. Later amendments were not read.
21. nidirect, "Vehicle maintenance, safety and security" and "Penalties", annexes to the Highway Code for Northern Ireland, modified 21 September 2026. Read: both in full, 26 September 2026.
22. nidirect, "Maintaining your vehicle", modified 2 August 2023. Northern Ireland. Read: full text, 26 September 2026.
23. nidirect, "Fixed Penalties for motoring offences", modified 14 May 2026. Northern Ireland. Read: full text, 26 September 2026.
24. Road Vehicles (Construction and Use) Regulations 1986, introduction. Read: the enabling words, on the live page, 26 September 2026. The provision of the 1988 Act that carries earlier regulations over was not read.
25. The Highway Code, "Annex 6. Vehicle maintenance, safety and security", updated 29 January 2022. Great Britain. Read: full text through the GOV.UK content API, 26 September 2026. The line used here is advice, not a MUST rule.
26. Road Vehicles (Construction and Use) Regulations 1986, regulation 18 and regulation 61, as amended. England, Wales and Scotland. Read: regulation 18(1) and regulation 61(1), on the live pages, 26 September 2026.