The gap between petrol and diesel prices has hit a record high due to Russia reducing gas supplies.
Analysis of Government figures by the PA news agency and the RAC Foundation found the average price of a litre of diesel is nearly 17p more expensive than petrol.
Steve Gooding, director of the RAC Foundation, said the difference is mainly due to an increase in the amount of diesel being used for heating and power generation in continental Europe because Russia has cut gas exports.
Figures from the Department for Business, Energy and Industrial Strategy show average pump prices for a litre of fuel on Monday were 180.3p for diesel and 163.8p for petrol.
This means filling a typical 55-litre family diesel car is around £9 more expensive than for petrol models.
The price difference is the largest in records dating back to June 2003.
Diesel has only cost around 5p per litre more than petrol on average since then.
Mr Gooding 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.
“The bad news for UK diesel drivers – and the diesel-truck-dependent UK freight industry – is that, with winter only just starting and the war in Ukraine showing no sign of ending, the sizeable gap between diesel and petrol pump prices is likely to continue for several months to come even if the cost of oil drops.”