Drink-driving is the oldest road safety topic there is, and it still ends professional driving careers every week. GOV.UK’s guidance opens with the two facts that should frame every conversation about it: there are strict alcohol limits for drivers, and it is impossible to say exactly how many drinks those limits equal, because it is different for each person. Everything else in this article hangs off that second point.
The legal limits, expressed three ways:
| Level of alcohol | England, Wales and Northern Ireland | Scotland |
|---|---|---|
| Micrograms per 100ml of breath | 35 | 22 |
| Milligrammes per 100ml of blood | 80 | 50 |
| Milligrammes per 100ml of urine | 107 | 67 |
Two consequences follow from that table. First, Scotland’s limit is markedly lower - a driver legal in Carlisle can be illegal in Gretna, and cross-border runs are daily reality for plenty of fleets. Second, the limits are not targets to drive up to. They are the point past which the law stops debating impairment and simply convicts.
Drivers want a number of pints, and there isn’t one. The guidance lists what changes how alcohol affects you:
The same two drinks can produce different readings in the same person on different days. Any policy or pub wisdom built on a fixed number of drinks is built on sand, which is why professional drivers operate on the only number that is always safe: zero when driving.
Nothing in the limit table has a time of day attached. Alcohol clears at its own pace, and a driver who drank heavily until midnight can easily be over the limit at 7am - exactly when a trunking shift starts. The field where this bites hardest is not the evening out but the early start after it. Fleets that talk about drink-driving only in terms of “never drink and drive the same evening” miss the most common failure mode in the industry.
The guidance warns of strict penalties, and it adds a UK-wide point worth underlining: you cannot drive anywhere in the UK if you have been banned by any UK court for drink-driving. A ban in one nation is a ban in all four.
For a professional driver the sentence is only the start. A drink-driving conviction typically means the loss of the vocational entitlement that pays the mortgage, and for an operator it drags the driver’s conduct onto the operator’s desk: a driver caught over the limit in a liveried truck is a conversation about repute, systems and supervision that nobody wants to have at a public inquiry.
The limits also explain why the old “one per hour” folklore fails in both directions: a large person might stay legal where a smaller colleague would not, and either of them can tip over on an empty stomach or a short night’s sleep. There is no version of the maths a driver can do reliably in a pub car park.
Strong fleets go further than the law and make it simple:
The guidance’s own framing is the best briefing: there are strict limits, and nobody can tell you how many drinks keep you under them, because it is different for every person and every day. If the answer matters - and for a professional driver it matters more than for anyone - the only safe unit is none.
Drink-driving law has not changed much in decades, but fleets keep losing good people to it, usually in the morning, usually after a night they thought was fine. The fix is not a better rule of thumb. It is no rule of thumb at all.