Diesel slips back below £2, and the maths has not caught up

Diesel averaged 199.90p a litre on Friday 9 October, according to the RAC's fuel price statement, which puts the average back under £2 a week after it crossed the mark. Petrol averaged 174.79p on the same day. The daily move on diesel was 0.11p, so the distance between the headline and the threshold is about a tenth of a penny.

That is worth holding on to for a moment. "Diesel back below £2" is true, and it is also a rounding error with a press release attached. On a 55-litre fill the 0.11p is worth about 6p. The number that matters to a household is not the threshold. It is the 40% that has been added since the end of February.

How far the price has travelled

The RAC's table runs from 28 February 2026, the point at which the US-Iran conflict began to move the market. Diesel stood at 142.38p that day and sits at 199.90p now, a rise of 57.5p or 40.4%. Petrol has gone from 132.83p to 174.79p, up 42.0p or 31.6%. Both percentages are printed on the statement and both check out against the two dates.

The cash difference lands in the tank. The RAC puts the extra cost of filling a family-sized car at £31 for diesel and £23 for petrol compared with late February, which is the figure most households will recognise from their own bank statements rather than from a price table.

We covered the crossing itself in the day diesel hit £2 and the approach to it in our September piece. This is the piece about what happens after a record is set: the slow drift back towards the line, and the question of whether any of it matters.

What a litre is made of

The RAC Foundation's analysis of the government's Fuel Finder data, published at the end of September, sets out where the money goes. Fuel duty is 52.95p a litre on both fuels, and 86p of a £2 litre, or 43%, reaches the Treasury once VAT is added. Petrol carries 82p of its 174.7p, or 47%.

That structure explains why a small dip does not become a small saving. Duty is a fixed cash amount per litre, so it does not fall when the product does. VAT is charged on the fuel and on the duty, so it falls in proportion. The tax share of a litre therefore barely moves as the price drifts: 43% at £2, still about 43% at 199.90p, while the part that reflects the oil price gives back a tenth of a penny.

The scale of the exposure is not small either. The Foundation counts 10.3 million diesel cars and 4.6 million diesel vans on UK roads, with a further 18.9 million petrol cars. Every one of them is paying a price that would have been a record before this year.

Pence per mile, which is the number that survives

A 45mpg diesel covers about 9.9 miles on a litre, so 199.90p works out at roughly 20p a mile in fuel alone. A 10,000-mile year is about £2,020 and a 15,000-mile year is about £3,030, before servicing, insurance or tyres.

The electric side of that comparison has barely moved. Ofgem's price cap unit rates put the average direct debit electricity rate at 26.32p per kWh for the quarter from 1 October, up from 26.11p. That is a rise of 0.8%, against 40.4% on diesel. A car using 4.5 miles per kWh costs about 5.8p a mile at home on the capped rate, or £58.49 per 1,000 miles, and the arithmetic behind that was set out on the day the new cap started.

Put the two together. The same 10,000 miles that costs about £2,020 in diesel costs about £585 in home-charged electricity. Diesel is up 40.4% since February and domestic electricity is up 0.8%, and that pairing is the whole story of the past seven months in two numbers.

Where the relief does not reach

Two caveats are worth stating plainly, because the comparison above is the best case for electric and the average case for diesel.

The first is access. A home-charged mile needs somewhere to plug in. Public charging sits outside the price cap entirely: rapid rates are set by the operator and the landowner, and the spread between a driveway tariff and a motorway charger is the widest part of the electric cost range. A driver renting a flat with no off-street parking is not making the £585 comparison at all, which is why the public and home price gap matters as much as the pump price does.

The second is the car. A 55mpg diesel at 199.90p is about 16.5p a mile and a 35mpg one is about 26p. The average hides a spread of more than 9p a mile, which is larger than the entire dip. Anyone comparing their own diesel with an electric car should start from their own mpg rather than the national average.

The next move is not in the price

The RAC's head of policy, Simon Williams, said the country is "a long way from being out of the woods" on fuel prices, and pointed drivers towards the Budget this month. He also set out what happens without action there: 3p a litre of duty is scheduled to return on 1 January, with another 2p on 1 March. The RAC's ask is an extension and increase of the existing duty cut, or a VAT reduction along the lines of the one applied to domestic electricity.

The Budget has not happened, so none of that is a prediction of what it will contain. What is already true is the schedule, and the RAC expects 2026 to end as the second most expensive year on record for drivers.

What to take from it

Diesel at 199.90p is not a recovery. It is a pause at a level that would have been a record in any other year, seven months after a 40% rise, with two duty increases already timetabled and a Budget that may or may not change them.

If you are choosing between a diesel and an electric car on running costs, work from pence per mile and your own annual mileage rather than from the price on the forecourt sign, because the gap between the two has widened since February rather than closed. If you already run a diesel and cannot change, the honest position is that a tenth of a penny changes nothing at all. The only thing on the near horizon that could is a fiscal decision that has not been made yet.