The drop in the value of the pound added 7p per liter to motorists' fuel bills within a year.
A review by the Competition and Markets Authority (CMA) found that the "main drivers" of higher fuel costs were higher oil prices and improved profit margins at refineries.
A report published in July said high oil prices, usually measured in US dollars, had caused UK fuel prices to rise by about 20 pence a liter in the 12 months to June 27.
The fuel bill added 7p per liter as the pound weakened against the dollar over the same period.
This is a record rate above the 5-pence liter tax that the Treasury Department introduced in March.
The CMA found that retailers were mostly continuing the cuts.
The latest government figures show that the average price of petrol in the UK is around £1.62, while diesel is around £1.81 a liter.
A year ago petrol was £1.37 and diesel £1.41
Sterling hit a record low against the dollar on September 23 after Chancellor Kwasi Kwarteng's mini-budget.
It has since recovered, but is still 18% weaker than last year.
Steve Gooding, director of car research charity RAC, said: “The CMA believes the 5-pence cuts seen earlier this year have been passed on to motorists but have been swallowed up by the massive drop in the value of the pound; little consolation for motorists. Who are facing high prices
“While fuel prices have rebounded strongly in recent weeks, higher crude oil prices, higher refining margins, OPEC (Organization of Petroleum Exporting Countries) production cuts and increased volatility in currency markets point to a looming financial storm cloud, all the more severe. For diesel drivers who are already facing 20p per liter of gasoline premium.
“Given all the other pressures the Treasury has to deal with, another rate cut is unlikely any time soon.
“If anything happens, it has to be big to have a huge impact on the price of the pump.”
The Capital Markets Authority also found that the widening gap between crude oil prices entering refineries and the wholesale price of gasoline and diesel increased by 24 pumps per liter during the past year.
