Drivers benefited from a 6p per litre fall in petrol prices last month, new figures show.
The average price of the fuel at UK forecourts decreased from 146.7p on December 1 to 140.6p on December 31, the RAC said.
It was the second consecutive monthly price cut.
This has brought petrol prices down to a level last seen in early February 2022, before Russia’s invasion of Ukraine sparked a surge in the cost of oil.
The average price of a litre of diesel fell from 154.3p to 149.2p in December.
But the RAC said pump prices should be reduced further as the average supermarket margin on fuel was 13p per litre last month, which is more than double what it was in 2021.
The motoring services company also noted that average fuel prices in Northern Ireland at the end of the month were 135.3p per litre for petrol and 144.2p per litre for diesel.
In July last year, competition watchdog the Competition and Markets Authority said pump prices are generally lower in Northern Ireland than the rest of the UK because of competition from forecourts in the Republic of Ireland.
RAC fuel spokesman Simon Williams said: “It’s clearly good news that both petrol and diesel came down substantially in December.
“While we’re starting the year paying much less at the pumps than we have done, it’s still galling to know that drivers aren’t being charged a fair price in comparison to Northern Ireland where the very same petrol and diesel is at least 5p a litre cheaper.
“It’s surely impossible to argue that competition is working properly if prices are so vastly different in two parts of the UK.
“We continue to call on the biggest retailers to play fair with drivers and lower their prices to match what’s being charged in Northern Ireland.
“We also urge Energy Security Secretary Claire Coutinho, who is on a mission to bring greater transparency to fuel pricing following the Competition and Markets Authority’s investigation concluding drivers were overcharged to the tune of £900 million in 2022, to ask the supermarkets why they won’t charge similar prices to the averages seen across Northern Ireland.”
A Department for Energy Security and Net Zero spokesperson said: “The drop in petrol prices in the run-up to Christmas was good news for many hardworking families driving hundreds of miles across the country.
“We want fuel prices to stay down for 2024 and beyond. That is why the Government is giving the competition watchdog tough new powers to oversee the market and make sure retailers pass on savings.
“This stance is working, and we will continue progressing plans for fuel retailers to share up-to-date price information that will help customers to easily shop around for deals.”