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Diesel Is Knocking on £2 a Litre
Diesel averages 197.31p and the RAC expects the record to fall. What record fuel prices mean for the drivers who cannot yet switch away from the pump.
Diesel is 1.78p away from the most expensive litre in British history. The average pump price hit 197.31p on 23 September, closing on the 199.09p record set on 25 June 2022, and many forecourts are already charging more than the old record. Two days later the average stood at 198.32p, with the RAC saying the record would "almost certainly be surpassed over the weekend". For the millions of drivers who depend on diesel and cannot simply switch tomorrow, this is a running-cost problem that lands now, not in the next budget cycle.
How we got here
The cause is the conflict that began at the end of February between the US and Iran, which has driven up the cost of oil and wholesale fuel. The RAC's numbers show the scale: diesel was 142.38p a litre on 28 February, and is up 54.9p a litre since, a rise of 38.6%. Petrol has risen too, but less, from 132.83p to 173.08p over the same period, up 30.3%. The gap between the two fuels has widened because wholesale diesel supplies are tighter, and diesel's price reflects that squeeze more sharply.
The fill-up arithmetic is what most drivers feel first. Filling a 55-litre diesel car now costs £108.52, which is £30 more than it did before the conflict began. The equivalent petrol fill-up costs about £95, roughly £22 more. For a high-mileage driver getting through two tanks a week, those differences compound into four figures across a year.
RAC head of policy Simon Williams put the outlook bluntly when the average was still under the record: "The question facing drivers is no longer 'when will the average price exceed 199.09p?' but 'how far above £2 a litre will it climb?'". In his view, only a sudden and sustained drop in the cost of oil prevents an average above £2, and he judged that unlikely. Once the record falls, nothing anchors diesel below the psychological £2 line except the oil market itself.
What it costs the drivers who cannot switch
It is worth being fair to diesel before piling on. For high-mileage drivers, towers of caravans and trailers, rural drivers facing long gaps between chargers, and anyone pulling heavy loads for a living, a modern diesel remains the tool the job actually requires. Nobody should feel daft for running one in 2026. But the economics have shifted under their feet, and it is worth quantifying by how much.
Take a driver covering 15,000 miles a year at 45mpg. At 197.31p a litre, their fuel bill is now running at roughly £2,990 a year, about £830 more than the same driving cost at the 142.38p diesel price of late February. That is not a rounding error in a household or business budget, and it arrives alongside higher petrol prices for the family's second car.
There is also the tax question. Fuel duty has been cut by 5p a litre, and that relief now runs to 31 December 2026, with the main rate at 52.95p. The government has extended the cut repeatedly since 2022, and each extension costs the Treasury money it will eventually want back. Record pump prices make the duty debate louder in both directions, and our analysis of fuel duty versus electric motoring costs looks at how the comparison is drawn.
The quiet repricing of the used market
High fuel prices do not stop at the forecourt; they flow into what cars are worth. The used market is already showing the pattern: in September's early data, values of used diesel cars at three years old were slipping while hybrid and electric values firmed, and our used EV price gap analysis tracks how that trade-in difference is closing. A diesel owner looking to jump is selling into a softening market, which is precisely when making the switch is cheapest to do.
That matters because the running-cost alternative has never been sharper. Home charging on an EV tariff costs a fraction of the per-mile cost of diesel at current pump prices, and even public rapid charging now compares favourably with a diesel doing motorway miles. The RAC's own numbers put the scale of the shift in perspective: a diesel driver spending roughly £250 a month on fuel alone is paying more each month than the finance cost of many small electric cars.
What to do about it now
For diesel drivers not ready to switch, the practical levers are the boring ones that always work. Shop the price: the gap between the dearest and cheapest forecourts in any area is routinely more than 10p a litre, and supermarkets and motorway services sit at opposite ends of it. Drive the fills you already do at gentler revs, since diesel economy is unusually sensitive to throttle. And if you tow or carry heavy loads, remember that a loaded roof or an underinflated set of tyres costs more per mile on a diesel than on any other fuel.
For those whose contracts or finances put the switch a year or two out, the honest read is that diesel's brief return to cheapness is over for good. Wholesale pressure from the conflict sits on top of a long-term policy direction that taxes combustion fuel ever harder. The drivers best positioned are the ones who treat the current record prices not as an anomaly to wait out but as the new baseline, and plan the transition on their own schedule rather than the pump's. The arithmetic behind that decision, including the per-mile tax changes coming for electric cars, is set out in our piece on the 3p-per-mile question.