Cornwall’s diesel drivers face the bigger bill when fuel duty thaws

If you’ve got a diesel on the drive in Cornwall, you’re in good company. You’re also the driver this week’s Budget will catch hardest, though not for another 20 months.

Diesels make up 50.8% of the cars and vans that went through an MOT in the TR postcode area last year. That’s the 8th highest share anywhere in Britain, according to analysis of DVSA’s 2025 MOT records by CarCostCheck. And when fuel duty goes up, diesels pay more than petrol cars.

How the fuel duty change works

The Budget on Wednesday 28 October kept fuel duty frozen until the end of June 2027. The rises that had been due in January and March were scrapped.

But the freeze doesn’t ease off gradually. It ends all at once on 1 July 2027, when duty is due to go up by 7.64p a litre. On a typical tank, that’s about £5 more every time you fill up.

What it will cost Cornwall motorists

For a typical petrol car in Cornwall, the rise works out at about £56 a year, a little below the national figure of £57.

For a diesel it’s about £72 a year. The national figure is £78.

Why diesels pay more

Diesels usually cover more miles than petrol cars, so they burn through more duty-paying fuel over a year. With more than half of local cars and vans running on diesel, more Cornish households will be paying the bigger bill.

The calculation uses the average annual mileage of cars and light vans (MOT class 4) at their 2025 MOT, assuming 45mpg for petrol and 50mpg for diesel, with duty rates from HMRC’s Budget 2026 rate tables.

Is a diesel still worth it?

There’s a twist in the Cornwall figures. Diesels here are popular, but they cover fewer miles than the average diesel in Britain.

The founder of CarCostCheck said: “More than half of the cars and vans that went through an MOT in Cornwall last year were diesels, yet diesels here do fewer miles than the average diesel in Britain. When you next change car, it is worth working out whether a diesel still pays for itself on the miles you actually do.”