Every driver believes motorway fuel is a rip-off, and every driver suspects the station two streets away is cheaper. Until this year nobody could prove either claim at national scale, because the prices were never published. Britain made publication compulsory in February 2026. By April its competition regulator had the numbers, and they are larger than most people would have guessed.
The motorway premium, measured
Using data collected between 11 March and 13 April 2026, the Competition and Markets Authority found motorway forecourts charging up to 26 pence per litre more for petrol than non-motorway sites: roughly £14 on a 55-litre tank. For diesel the gap reached 17 pence per litre, about £9 a tank.
Set that against the retailer's whole margin. Across February and March 2026 average fuel margins ran at 10.3 and 10.7 pence per litre, close to the 2025 average of 10.7ppl. So the motorway premium at its widest is more than twice a typical retail margin. It is not a slightly fatter version of an ordinary forecourt's economics; it is a different business model.
The reasons are structural rather than sinister. A motorway site is a captive location with limited sites per stretch, sold or leased on long concessions, obliged to open around the clock, staffed accordingly, and reached by drivers who by definition cannot easily compare. None of that is a conspiracy. But it does mean the premium is a permanent feature of where you are standing, not a temporary local price war, and permanent features are the ones worth planning around.
The finding nobody expected
The motorway gap confirms a suspicion. The other number in the same report overturns an assumption.
Looking at a single day, 7 April 2026, the CMA compared stations within a ten-minute drive of each other. In Sheffield, petrol varied by 16 pence per litre: about £9 a tank between forecourts a few minutes apart. In Wakefield, diesel varied by 17ppl. Trafford, Sunderland and Hammersmith each showed up to £7 a tank available to anyone who drove past the first station. Aberdeen, by contrast, showed only about £3.
By comparison, choosing a supermarket over a non-supermarket forecourt saved up to 8ppl on petrol (around £4.40 a tank) and up to 11ppl on diesel (around £6).
Read those two together. The variation between neighbouring stations in one city was larger than the variation between supermarket and non-supermarket brands nationally. The rule of thumb most drivers carry (supermarkets are cheap, everyone else is not) is worth less than simply checking the specific forecourts near you. And the size of that local gap is why the regulator's own reading is that the market shows a lack of fully effective competition.
Why this could not be known before
It is worth being precise about what changed, because it was not the prices. It was the visibility.
Before February 2026 there was no obligation on a UK retailer to publish anything. Price comparisons relied on voluntary submissions, crowdsourcing and scraping, sources that are patchy in exactly the places where competition is weakest, because a forecourt with no nearby rival also tends to have fewer people bothering to report it. You cannot measure a market's dispersion with a sample that thins out wherever the dispersion is widest.
Mandatory reporting removes that bias at a stroke. Every station, every price change, within thirty minutes. Only then can a regulator say with confidence that two forecourts ten minutes apart differ by 16 pence.
The coverage number worth remembering
Here is the honest complication, and it matters more than the headline figures.
By mid-April 2026, 8,074 forecourts had registered with the scheme, excellent progress from roughly 6,200 at launch. But the number actually reporting prices on a given day reached up to 4,712.
Registration is not participation. Something under three in five stations were supplying live prices on a typical day, several months into a legally mandatory scheme backed by a regulator with the power to fine. Not through defiance: a small independent forecourt has to connect a till system to a national feed and keep it running, and that is a real engineering burden for a business with no IT department.
This is the most useful single fact in the whole story for anyone judging a fuel app. Complete live pricing is extremely hard even when it is the law. Any product claiming it everywhere, voluntarily, is describing an ambition.
What to do with this
- Fill up before the motorway, not on it. Up to £14 a tank is worth a few minutes of planning. The premium does not fluctuate away: it is built into the location.
- Check the actual forecourts near you, not the brand. A 16p local spread beats an 8p brand rule. The cheap station near you may well not be the one your instinct expects.
- Do not drive across a city for it. Ten minutes was the regulator's own comparison radius, and it is a sensible one. Beyond that the fuel burned and the time spent eat the saving.
- Expect your area to differ. Sheffield showed £9 of headroom and Aberdeen about £3. How much shopping around is worth depends entirely on local competition, so it is worth learning your own area once rather than assuming a national rule.
- Ask where a price came from, and when. In the UK there is now a statutory answer. Almost everywhere else there is not, and the honest options are a recent human report or nothing.
What this means for the rest of the world
The temptation is to read this as a UK story. It is more useful read as a controlled experiment that the rest of the world has not run.
A 16-pence gap between neighbouring stations almost certainly exists in most countries. It has simply never been measured, because nobody was obliged to publish. Drivers everywhere are making the same decisions with less information than a British driver had in April 2026, and the gap between what they pay and what they could pay is invisible rather than absent.
We cannot fix that with software. What we can do is refuse to paper over it: show the prices real drivers report, stamped with the minute they reported them, and show nothing where nobody has looked recently. Britain's experience says even a legal mandate reaches about three-fifths of stations on a given day. An honest map should look like that reality (well covered in some places, empty in others) rather than uniformly confident everywhere.