The supermarket will run the deal until Sunday 9 October and it means anyone spending £40 in store will receive a coupon offering 5p off every litre of fuel.

It can be spent at all 339 Morrisons petrol stations across the UK – bar franchised Morrisons Daily petrol stations – until Sunday 16 October.

As you’d expect, there are certain items which are excluded from the £40 spend, such as tobacco, lottery tickets, gift vouchers, formula milk, and mobile phone top-ups, so check the terms first.

Morrisons cuts prices on 150 items

Morrisons – which was recently knocked out of the ‘big four’ chains by budget challenger Aldi – has also reduced the price of 150 of its most popular products.

It said the lower prices cover nearly 6% of Morrisons total volume sales and offer an average saving of 14% per product.

Rachel Eyre, chief customer & marketing officer at Morrisons, said: “Fuel prices are one of the biggest expenses people across the UK are facing as the cost of living increases.

“We want to help our customers save money wherever we can and hope this offer can help make budgets go a little further.”

Record gap between petrol and diesel

According to RAC fuel watch, the average price of a litre of unleaded stood at 162.96p while diesel stood at 180.22p on 28 September. Diesel is now 17p a litre more expensive than petrol.

It said this is the biggest gap between petrol and diesel pump prices since at least 2000.

RAC fuel spokesman, Simon Williams, said: “While average prices of both petrol and diesel have dropped considerably from the all-time highs of the summer, diesel is now a record 17p a litre more expensive than unleaded.

“The gap between the two fuels is normally around 4p a litre but this has widened since Russia invaded Ukraine. Prior to this, diesel had only ever been as much as 11p dearer than petrol back in August 2015. Looking at the two fuels on the wholesale market, the gap is currently 20p a litre but has been as high as 27p at the end of August this year. Despite this, the gap at the pumps in the following fortnight – the time it generally takes for price changes on the wholesale market to be fully reflected on the UK’s forecourts – only averaged 14p.”

Williams explained that several factors are combining to make diesel more expensive. While the EU is not set to ban Russian diesel imports until February 2023, the UK has already done so. “This is significant as we used to import a third of our diesel from Russia”, he said.

“In addition, European demand for gas oil – red diesel – tends to go up at this time of year as it is commonly used for heating. And this is greater this autumn as Europe is looking to lessen its reliance on gas and, as a result, is boosting its diesel supplies to get through the winter,” he added.

Tough time to be a diesel driver

Williams added: “This all means it’s continuing to be a tough time to be a diesel driver. Fortunately, the average price is now almost 20p a litre less than it was at its high of 199.09p in late June. But with the pound recently dropping to record lows against the dollar all we would need is for the price of oil to start rising from its current level of around $90 a barrel to cause both diesel and petrol prices to climb back up again.

“Diesel has occasionally been sold for less than petrol with the biggest gap being 3p in August 2015 when petrol averaged 114p and diesel 111p.”