In the UK last month, the average price of diesel decreased by a record 12p per litre, according to the RAC.
According to the group, pump prices decreased from about £1.59 to £1.47, saving families £6.50 on gas for a family car.
Since it started keeping track of prices in 2000, the RAC claimed that the decrease was the largest monthly drop it had ever witnessed.
However, the motoring association claimed that because wholesale prices were lower, the price reduction was "long overdue" and "smaller than it should be.".
In response to declining wholesale costs, "big cuts" in diesel prices, according to the British Retail Consortium, which represents supermarkets.
Following a seven-month streak of declines, diesel prices are now more than 25% lower than their peak in 2022.
After oil prices spiked in the wake of Russia's invasion of Ukraine, the cost of gasoline reached a record high of £1.199 per litre last summer.
Additionally, the cost of gasoline has been steadily declining since that time, dropping from an average of £1.16 to £1.43 last month, according to RAC statistics.
The motoring group asserts that despite the fact that prices were significantly lower in Northern Ireland, they have not decreased as quickly or substantially as they should have.
The RAC claimed that since the cost of diesel at the wholesale level had been less than that of gasoline for ten weeks, the reduction should have been more pronounced to accurately reflect changes in the market.
In May, the Competition and Markets Authority (CMA) declared it was looking into fuel prices and whether a "failure in competition" had resulted in drivers paying too much.
The watchdog stated that it was "concerned" with the consistently higher margins on diesel compared to gasoline so far this year.
It claimed that the information it had so far suggested that at least one supermarket had set a higher goal for its profit margin on fuel prices in 2022, which may have prompted competitors to raise prices as well.
After urging price decreases recently, the RAC noted that it was "ironic" that the most recent price reductions "finally came in the two weeks following the Competition and Markets Authority's announcement.".
The CMA will undoubtedly think about what happened to the price of diesel in May, Mr. Williams predicted. "We fervently hope that the pump price reductions carry on as they should. ".
The Petrol Retailers Association, which represents thousands of independent forecourts, is advised to "shop around," according to Gordon Balmer, executive director of the association.
"The ongoing conflict in Ukraine continues to have an impact on gasoline and diesel prices, as the CMA noted. Independent forecourts frequently undercut supermarkets on price because of how dynamic the market is, he continued.
Over initial worries that retailers and forecourts were failing to pass on a 5p fuel duty cut to motorists, a separate review of the fuel market has been ongoing for a number of months.
