It comes as an impending review by the Competition and Markets Authority into the weakening competition in fuel prices.
The CMA said while the majority of fuel price increases were due to the war in Ukraine pushing up wholesale costs, “indications are that higher pump prices cannot be attributed solely to factors outside the control of the retailers”.
It added that average 2022 supermarket pump prices seemed to be around 5p per litre more expensive than they would have been had their average percentage margins remained at 2019 levels.
There are concerns diesel drivers, who are already under pressure to comply with impending net zero and local low-emission zone targets, face weaker competition in diesel prices. The RAC said the average price in Northern Ireland was 138.49p per litre, 8.5p cheaper than the average rate in the UK.
Simon Williams, of the RAC, said the price difference was “galling”. Price data showed Northern Irish drivers were still paying 10p per litre less than UK drivers in April.
He added: “This points to a more transparent and competitive fuel market there, something drivers in the rest of the UK would very much like to see, particularly with money being so tight in the cost of living crisis.”
Mr Williams maintained retailers with lower prices “were still making money”, suggesting UK supermarkets could drop prices even further.
He said: “If greater transparency returns to the market we ought to be heading for an average diesel price of 137p, similar to what drivers are paying in Northern Ireland – and a price the UK as a whole hasn’t seen since September 2021.”
The CMA said it had not been satisfied with evidence provided by supermarkets in its initial study and is set to conduct formal interviews with senior management this month. A report is expected in July.
