The seven sins: what actually counts as a Most Serious Infringement
A driver on a standard nine-hour day who keeps going to 13 hours 30 minutes without taking a break or an uninterrupted rest of at least 4.5 hours has committed one of the seven Most Serious Infringements in UK road transport law.¹
Most operators and transport managers know the initials MSI. So here's the question this piece sets out to answer: what exactly are the seven Most Serious Infringements, where precisely is each line drawn, and what does the law make happen when one is recorded against an operator or transport manager?
The list itself is short. It sits in Annex IV of Regulation (EC) No 1071/2009, the regulation that sets the conditions for being a road transport operator, as it now applies in UK law.² The Senior Traffic Commissioner reproduces it at paragraph 36 of Statutory Document No. 1 on good repute and fitness (Version 18.0, March 2025), and confirms at paragraph 35 that commissioners must consider these infringements when assessing good repute.³ The Commission, when it later built a wider grading of serious infringements in Regulation 2016/403, used the Annex IV list as the upper reference point against which every other infringement was measured.⁴ These are not the only breaches that can cost an operator its repute. They are the top of the scale.
What stands out on reading the seven is how little of the list calls for judgement. Most of it is arithmetic.
Sin one: the hours line is a percentage, not a feeling
The first MSI has two limbs. Exceeding the six-day or fortnightly driving limits by 25 per cent or more is an MSI. So is exceeding the daily driving limit by 50 per cent or more, during a daily working period, without taking a break or without an uninterrupted rest of at least 4.5 hours.²
The limits those percentages apply to are set by the drivers' hours rules: nine hours of driving a day, which may be extended to ten no more than twice a week, 56 hours in a week, and 90 hours across any two consecutive weeks.⁵ The arithmetic that follows is mine. Taking the 56-hour weekly limit as the reference for the six-day test, 56 × 1.25 = 70 hours. Across a fortnight, 90 × 1.25 = 112.5 hours. On a normal day, 9 × 1.5 = 13.5 hours, and on an extended day, 10 × 1.5 = 15 hours. The UK's version of Regulation 2016/403 has, since 1 January 2026, stated the two daily figures in exactly those terms, 13h30 and 15h.¹
Two points are worth drawing out. The daily limb is not simply a long day; it is a long day combined with the absence of the break or rest that would otherwise have broken it up. And the weekly and fortnightly limbs are cumulative, which means they can be reached through a pattern of individually unremarkable days rather than one dramatic one.
Sins two and six: the record, not the road
The second MSI covers not having a tachograph or speed limiter, using a fraudulent device able to alter what the recording equipment or speed limiter records, or falsifying record sheets or data downloaded from the tachograph or driver card. The sixth covers driving with a driver card that has been falsified, that belongs to someone else, or that was obtained on the basis of false declarations or forged documents.²
This next part is opinion, so I'll flag it as such. These two belong together, and they deserve their place at the top of the scale for a reason that has nothing to do with how dangerous any single journey was. Every other check in the system, the hours thresholds above included, depends on the record being genuine. A driver who exceeds the daily limit by half can only be caught if the tachograph data are honest. Tampering with the record does not just add one more breach; it removes the regulator's ability to see the others. Unlike the hours and weight sins, these two have no percentage attached. There is no margin of falsification that is acceptable.
Sins three and four: defects and dangerous goods count when the vehicle is stopped
The third MSI is driving without a valid roadworthiness certificate where one is required, or driving with a very serious deficiency in, among other things, the braking system, steering linkages, wheels and tyres, suspension or chassis, where that deficiency creates such an immediate risk to road safety that it leads to a decision to immobilise the vehicle.²
The fourth concerns dangerous goods: carrying goods that are prohibited for transport, carrying them in a prohibited or non-approved means of containment, or failing to identify them on the vehicle as dangerous goods, in each case endangering lives or the environment to such an extent that it leads to a decision to immobilise the vehicle.²
The common thread is the immobilisation test. Neither of these is triggered by a defect or a labelling error in the abstract. The deficiency or the breach has to be serious enough that an examiner decides the vehicle cannot continue. That makes these two less arithmetical than the hours and weight sins, but still anchored to a concrete event rather than to a general impression of how well the vehicle was looked after.
One small oddity is worth noting here. Annex 1 of the Statutory Document, which sets the starting points for submissions to commissioners, lists use of vehicles "whilst uninsured or without MOT" and labels it as an MSI.³ Driving without a valid roadworthiness certificate is plainly in Annex IV. Insurance, on the face of the Annex IV text, is not in the text.
Sin five: no licence, no business being on the road
The fifth MSI is carrying passengers or goods without holding a valid driving licence, or carrying by an undertaking that does not hold the required operator authorisation. The UK version of the text originally referred to a valid Community licence. On 1 April 2025 its wording was extended to name, explicitly, a valid PSV operator's licence, a valid bus operator's licence and a valid operator's licence for the international carriage of passengers by road.²
Of the seven, this is the one most directly about entitlement rather than conduct. It does not ask how well the journey was run. It asks whether the person driving, or the business operating, had any right to be doing it at all.
Sin seven: the weight line moves with the plate
The seventh MSI is carrying goods that exceed the maximum permissible laden mass by 20 per cent or more for vehicles whose permissible laden weight is over 12 tonnes, and by 25 per cent or more for vehicles at or below 12 tonnes.²
Because the threshold is a percentage of the plated weight, the line moves with the vehicle. Taking two illustrative plated weights, and again the arithmetic is mine, a vehicle plated at 44 tonnes crosses the line at 44 × 1.20 = 52.8 tonnes, which is 8.8 tonnes over. A vehicle plated at 7.5 tonnes crosses it at 7.5 × 1.25 = 9.375 tonnes, which is 1.875 tonnes over. Lighter vehicles get the larger percentage margin, but the absolute margin is far smaller, and on a small vehicle a few extra pallets can close it.
A bright line that does not switch anything off by itself
The most common misunderstanding about MSIs is that one automatically ends a licence. It does not. Where an operator or transport manager has been convicted of a serious criminal offence, or has incurred a penalty for an MSI, in the UK or in one or more EU Member States, Article 6(2)(a) of the Regulation requires the commissioner to carry out an appropriate and timely administrative procedure, which may include a check at the operator's premises. That procedure has to decide whether, because of the specific circumstances, losing good repute would be a disproportionate response. If it would, the commissioner may decide repute is unaffected, and the reasons must be recorded. If it would not, the conviction or penalty leads to the loss of good repute.⁶
So an MSI does not revoke anything by itself, but it reverses the default. Without a reasoned finding of disproportionality, repute is lost. The Statutory Document adds a further layer at paragraph 85: where a commissioner decides it is not proportionate to call the matter to a public inquiry at all, the reasons must be fully recorded.³ Discretion is permitted at every stage, and at every stage it has to leave a written trail.
The case for discretion
There is a strong argument that the bright lines are, if anything, too bright, and it deserves a fair hearing. An automatic loss of repute for every MSI would punish operators for the conduct of a single driver, however good their systems. A haulier running a large fleet with sound tachograph analysis, disciplined follow-up and honest record-keeping can still find one driver using someone else's card. Revoking that licence would remove a compliant operator from the market and protect nobody. The disproportionality procedure exists precisely to tell that operator apart from one whose systems invited the breach.
I think that argument is largely right, and the law agrees with it, which is why the procedure exists. The point I would add is that the sharpness of the lines and the flexibility of the response are not in tension. The lines make it clear and arguable that a particular event happened. The procedure then decides what that event says about the operator. An operator who understands where the lines are is in a far better position to show, when it matters, that crossing one was an exception rather than a symptom.
The takeaway
The seven Most Serious Infringements are narrower and more measurable than their reputation suggests. Two of them, hours and weight, can be calculated in advance. An operator's analysis software and weighing checks can be set to flag those thresholds before a roadside check does. Two more, serious defects and dangerous goods, turn on whether the vehicle is immobilised. One is about whether the driver and the business had any right to be on the road. The last two, record tampering and card misuse, are the ones no threshold can catch, which is why they are the ones where driver supervision and download discipline matter most.
An MSI does not end a licence on its own, but it does put the burden on the operator's evidence: what systems were in place, what was done when the breach came to light, and whether it was a one-off or a pattern. Knowing the seven lines precisely is the cheapest part of that evidence to get right.
If you want a second pair of eyes on how your tachograph analysis, weighing checks or driver card controls line up against these seven thresholds, get in touch.
References
1. The European Registers of Road Transport Undertakings (Disclosure of Information) (Amendment) Regulations 2025, S.I. 2025/1202 (made 17 November 2025, in force 1 January 2026. Confirms that the UK version of Regulation 2016/403 now states the daily driving MSI thresholds as 13h30 and 15h.) 2. Regulation (EC) No 1071/2009, Annex IV: Most serious infringements (UK revised text) (legislation.gov.uk, viewed 19 October 2026. Confirms the seven MSIs and their thresholds, and the 1 April 2025 amendment to item 5 by S.I. 2024/1370 adding passenger operator licence wording.) 3. Senior Traffic Commissioner, Statutory Document No. 1: Good Repute and Fitness, Version 18.0 (Senior Traffic Commissioner, commencement March 2025. Confirms paragraphs 35, 36 and 85 and the Annex 1 wording on uninsured or un-MOT'd vehicles.) 4. Commission Regulation (EU) 2016/403 (UK revised text) (legislation.gov.uk. Confirms that the Annex IV MSIs were used as the upper reference threshold when grading the seriousness of other infringements.) 5. Regulation (EC) No 561/2006, Article 6 (UK revised text) (legislation.gov.uk, viewed 19 October 2026. Confirms the 9-hour daily limit extendable to 10 hours twice a week, the 56-hour weekly limit and the 90-hour two-week limit. The MSI thresholds derived from them in the article are my arithmetic, not figures stated in this source.) 6. Regulation (EC) No 1071/2009, Article 6 (UK revised text) (legislation.gov.uk, viewed 19 October 2026. Confirms the administrative procedure after a serious criminal offence or an MSI in the UK or a Member State, the disproportionality test, the recording of reasons, and loss of repute where no disproportionality finding is made.)