Record prices at the pumps, but diesel cars can still be cheaper to run than petrol

Up until around 10 years ago, successive UK governments encouraged people to buy diesel cars. And they did. In fact, nearly a third of new cars registered in the UK in 2004 were diesel. By 2011, this rose to more than half of new cars.

But diesel's popularity has plummeted in recent years. Today, diesel accounts for just 4% of new cars. So, what happened?

There’s no single reason for diesel’s decline, but changes in 2017 to how car tax is levied and subsequent tweaks to private and company car tax rules certainly took their toll. Then there are rising manufacturing costs, the fallout from Volkswagen’s ‘dieselgate’ scandal and diesel's reputation as the most polluting fuel type.

More recently, with the war in Iran, the UK's lack of refining capacity and high global demand, diesel car owners have faced sharp price rises at the pump. Diesel fuel now averages a record high of nearly £2 a litre.

But despite all this, a good diesel car can be cheaper to run (in fuel costs) than petrol.

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Expensive fuel, cheaper running costs

Our lab recently tested the entry-level 116hp diesel Volkswagen Golf manual hatchback, and it averaged 65.7mpg in our efficiency tests. That makes it around 15mpg more efficient than the petrol manual Golf we tested in 2025.

I’ve crunched the numbers to find out how much it would cost to run these two cars when driving around 6,000 miles per year and paying 174.7p for petrol and 200p for diesel (average UK prices for these fuels on 5 October).

Despite the high diesel pump price, the diesel Golf costs about £115 a year less to run than the petrol version.

In fact, the diesel Golf would only become more expensive to fuel if you paid 228p a litre for diesel while petrol remained at the current 174p a litre.

We also recently lab tested the diesel Seat Leon hatchback, and it too proved to be very efficient, averaging 60.1mpg. However, both Seat and Volkswagen removed the diesel Golf and Leon ranges from UK price lists earlier this year, and with only a few cars remaining in dealer stock, anyone looking to buy new diesel versions of these cars needs to act quickly.

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Diesel domination

While only 4% of new cars sold so far in 2026 have been exclusively diesel powered, one brand dominates the UK diesel car market: Land Rover.

Despite its range of petrol and petrol plug-in hybrid cars, Land Rover is the only brand that registers more diesel cars than any other fuel type.

Indeed, around 1.5% of all new cars registered in September 2026 were diesel Land Rovers, while the brand accounted for over 40% of diesel car registrations in the UK that month.

As the UK’s bestselling car brand, it’s not surprising that Volkswagen is one of the only other brands (along with Audi) that sells a lot of diesel cars in the UK.

That could change, as Volkswagen is discontinuing its large, diesel-powered Touareg SUV this year, which often leads to discounts as dealers try to sell remaining cars quickly.

Environmental concerns

There's no hiding from the fact that, like pure petrol cars, pure diesel cars simply can't match the environmental credentials of electric cars or even hybrid cars. To that end, no pure diesel or petrol car is, or likely ever will be, a Which? Eco Buy.

But, in terms of emissions, diesel has come a long way over the past decade.

Modern diesels rarely pollute like older models and often impress in our emissions tests (the 200hp Mazda CX-60 and Volkswagen Tayron diesels being two such cars). The diesel Genesis G70 Shooting Brake also performed better in our emissions test than the brand’s petrol G70 saloon.

And they’re getting better. We're yet to lab test it, but Audi recently re-engineered its 3.0 V6 diesel engine to improve its mild-hybrid element – the earlier iteration of this engine generally performed well in the Audi Q7 (2015-26).

Expert opinion: why a good diesel car is something to shout about

Dino Buratti, Which? senior researcher

For me, there’s a unique allure to diesel-powered cars. I find their raw pulling power unrivalled when compared to all but electric cars – there's something inherently special about how quickly a diesel car can accelerate.

But it’s also the smoothness of some large diesel engines that really appeals to me. Whether it’s the 3.3-litre engine found in Mazda’s largest SUVs, the 3-litre engine in many Land Rover SUVs or BMW’s 3-litre engine, diesels can be surprisingly quiet.

Modern six-cylinder engines tend to be mechanically more balanced than other types, and with the power spread across more cylinders, the driver (and passengers) benefit from a more hushed experience inside the car.

They may be unpopular and aren’t as environmentally friendly as electric cars on the road but, in my opinion, a good diesel car is something to shout about.

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