Why Diesel Now Costs UK Drivers 27.6p More Per Litre Than Petrol

• RAC Foundation analysis puts the current gap between diesel and petrol at 27.6p a litre, the widest it has been since at least 2003.
• The gap has widened since the Iran conflict pushed fuel prices up generally, with UK drivers paying more than £307 million extra for petrol and diesel combined since the US and Israel went to war with Iran.
• Diesel drivers are not seeing widespread profiteering by retailers, according to the same analysis, meaning the gap reflects wholesale market pricing rather than fuel stations quietly raising their own margin.

A Gap Not Seen This Century

Diesel has always traded close to petrol at the pump, often a few pence either side depending on the month. That relationship has broken down. RAC Foundation analysis now puts the gap at 27.6p a litre, with diesel the more expensive fuel, the widest margin between the two since at least 2003. For a driver with a 55-litre tank, that gap alone adds just over £15 to every fill-up compared with a petrol equivalent, before accounting for whatever the headline price itself is doing.

Why the Iran Conflict Is Driving the Price at the Pump

The war between the US and Israel on one side and Iran on the other has pushed global oil and refined fuel prices up since it began, and the RAC Foundation’s own figures put the additional cost to UK drivers at more than £307 million in extra spending on petrol and diesel combined since the conflict started. Diesel has been hit harder than petrol because of how European refining capacity is weighted and how diesel is traded internationally, which is part of why the usual small gap between the two fuels has stretched into something drivers are now noticing directly on the forecourt board.

The same analysis found the VAT the Treasury collects on that additional fuel spending has itself passed £100 million, since VAT is charged as a percentage of a higher pump price rather than a fixed amount. Every extra pound drivers pay at the pump during the conflict hands a cut straight back to the Exchequer on top of whatever a driver was already paying before prices rose.

Not Profiteering, According to the Foundation’s Own Check

It would be easy to assume fuel retailers are simply taking advantage of a crisis to pad their own margin, but the RAC Foundation’s analysis found little evidence of that happening in general. The gap tracks wholesale diesel costs rising faster than wholesale petrol costs, not UK forecourts adding an extra markup on diesel specifically. That distinction matters for any driver wondering whether switching petrol station chains would meaningfully close the gap: it generally will not, because the underlying wholesale cost is the same issue every retailer is working from.

The Government’s Own Fuel Price Tool Has Been Getting It Wrong

Separately, the same RAC Foundation research flagged significant errors in the government’s Fuel Finder service, the official tool meant to show live pump prices at thousands of filling stations across the UK. Drivers relying on Fuel Finder to shop around for the cheapest diesel in their area should treat its figures with some caution for now and cross-check against a station’s own forecourt price where practical, since an inaccurate live price defeats the entire purpose of a comparison tool.

Who Is Rethinking Diesel Because of This

Separate RAC research found three in ten UK drivers now say they are more likely to consider an electric vehicle next time around specifically because of the high fuel prices the conflict has brought. That is a notable shift in a fuel category, diesel, that was itself once sold as the economical choice for drivers covering high mileage. Whether that sentiment turns into actual purchasing decisions depends heavily on EV purchase costs and charging infrastructure rather than fuel prices alone, but it marks a real change in how diesel is being talked about by ordinary drivers rather than policy groups.

What Diesel Drivers Can Actually Do Right Now

Supermarket fuel, particularly from Asda, Tesco, Sainsbury’s and Morrisons, has typically undercut branded forecourts like BP, Shell and Esso by several pence a litre on both fuels, and that gap persists regardless of the wider diesel premium. Driving at a steadier, lower speed also helps more with diesel engines than people expect: the Department for Transport and RAC data both show fuel economy drops sharply above 60mph, so a driver doing 70mph instead of 60mph on a motorway run uses roughly 9% more fuel for the same distance. Combined with supermarket pricing, that is a genuine way to offset part of the extra 27.6p a litre without waiting for the market gap to close on its own.

Sources:

• RAC Foundation media centre