Diesel is now a record 17 pence per litre more expensive than petrol amid a surge in demand for diesel-powered generators to try and shore up electricity supplies.
It now costs £9 more to fill up an average diesel car in the UK compared to its petrol equivalent, after shortages of gas for power stations triggered a search for alternatives, particularly in Europe. Diesel is also in short supply amid efforts to shun Russia's supplies in the wake of its invasion of Ukraine.
Average pump prices for a litre of fuel were 180.3p for diesel on Monday and 163.8p for petrol, according to Government figures analysed by the PA news agency and the RAC Foundation.
Steve Gooding, director of the RAC Foundation, said: “In part, the huge gap is the product of a dip in global demand for petrol following the end of the so-called driving season in the United States.
“But more significant is the rising global demand for diesel, which is not only used as a road fuel but also, especially in continental Europe, as a method of heating and power generation and as a substitute for gas.
“Given that supplies from Russia have been cut back because of the war in Ukraine, this means there are a lot of people chasing less stock.”
He added the gap was likely to continue for several months, given the onset of winter and ongoing conflict in Ukraine.
Shortages of gas for power stations after Russia cut supplies to Europe have raised concerns about blackouts this winter. Several countries have taken steps to cut their energy use, with France turning off the lights on the Eiffel Tower earlier than usual, among other measures.
Diesel is used mostly for small-scale back-up generators designed to provide power when the grid fails, although it can also be used at a larger scale.
Both diesel and petrol prices hit record highs this summer. Diesel hit a record 199.09p in late June.
But Simon Williams, RAC fuel spokesman, said prices may climb again.
He said: “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 [£81] a barrel to cause both diesel and petrol prices to climb back up again.”