Supermarkets led the way with price rises in July as the average cost of petrol and diesel at the forecourt edged up by around 1ppl, according to RAC Fuel Watch.

Data shows that it was supermarkets that increased their prices the most in July, largely cancelling out the price cuts that they introduced just a few weeks earlier in June.

The price of an average litre of supermarket unleaded was up 1.64p to 125.34p, while diesel was up 1.62p to 128.88p. Motorway service areas increased the price of a litre of petrol by 1.19p to 146.09p, but left diesel almost unchanged at 148.14p.

RAC spokesperson Rod Dennis said: “July saw a return to rising prices at the UK’s forecourts, following some price cuts in the previous month. The rollercoaster effect of rising and falling prices that drivers will have witnessed in recent months is certainly in full swing.

“The volatility of the price of a barrel of oil, and in turn wholesale fuel prices, makes it difficult to determine where prices might go next. The announcement in June by the Organization of Petroleum Exporting Countries (OPEC) that its member countries would be increasing oil production could have been a trigger for further price falls, but the complicated disagreements between the United States – another big oil producer – and Iran and China are making prices go the other way. The result is a great deal of uncertainty on what might happen with UK fuel prices in the coming weeks.

“Fortunately for UK drivers, the pound remained stable against the US dollar – which is important as fuel, like oil, is traded in dollars. A weakening pound means it costs more for retailers to buy fuel in, which in turn tends to mean higher prices at the pumps.

“What is certain however is how much more expensive it is to fill up a car this summer compared to last year. At the end of July 2018 it cost £7.50 (12%) more to fill a 55-litre unleaded fuel tank compared to the same point in 2017, and £8.77 (14%) more to fill an equivalent diesel.”