The price of diesel has hit a 14-month high following Britain's decision to leave the European Union.
The nationwide average for diesel rose 1.9p per litre to 113.1p in September, the highest it has been since August last year.
The figures, which were released by The AA, indicate that petrol has also increased, seeing a rise of 1.6p to an average of 111.8p. The gap between the two has grown to 1.3p per litre.
The average price on supermarket forecourts of both unleaded and diesel has also risen, reaching 109p per litre last month.
The price hike is being blamed in part on the fact that oil prices hit $50 a barrel ahead of a possible halt in production.
The Organisation of Petroleum Exporting Countries announced last week that it might cut output by about one million barrels a day to 32.5 million. The final decision is due to be made at a meeting next month.
But the other big factor was the Brexit vote. Because oil is traded in American dollars, the pound's weakness against the currency since the vote has seen British retailers hit extra hard by high barrel costs.
The AA believes that the weakening pound alone has increased fuel prices by 4.5p.
The south-east of England and East Anglia had the highest average pump prices, while Northern Ireland saw the lowest increases.