In all other member states the rate of duty is lower on diesel than petrol.
Following the referendum on EU membership, prices in other EU countries are roughly 6% higher.
Steve Gooding, director of the RAC Foundation, said: “Talk of fuel prices going through the roof in the wake of a Brexit vote have proved to be fanciful with UK pump prices at essentially the same level they were before the vote.
“What might surprise drivers is that even allowing for the slump in the value of sterling they might still be better off buying diesel on the continent.
“The key message is that pump prices are determined by a whole host of factors. The exchange rate is one of them. The price of oil is another. But taxation is perhaps the most important of all.
“Before tax the UK actually has only the 22nd most expensive petrol in the 28 member states of the EU. With tax we jump to 8th in the league table. For diesel the UK is 23rd before tax, but we soar to the top of the list once tax is added.”