Motorists were hit by a record monthly hike in petrol prices in June.
RAC analysis found the average cost of a litre of the fuel at UK forecourts rose by 16.6p, from 174.8p to 191.4p.
It was the highest monthly increase in records dating back to 2000.
The rise in prices added more than £9 to the cost of filling a typical 55-litre family petrol car.
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Meanwhile average diesel prices rose by 15.6p per litre, ending the month at 199.1p.
The RAC warned higher pump prices were expected at the start of June due to the cost of oil rising in response to increased demand and continued supply concerns relating to the war in Ukraine.
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But five consecutive weeks of falling wholesale costs have not been reflected at the pumps.
Retailers have doubled their average profit margins from a long-term figure of around 6p per litre to 12p per litre, according to the RAC.
The organisation’s fuel spokesman Simon Williams said: “The rate at which pump prices have been rising over the last four weeks is hard to comprehend.
“Not a day in June went by when petrol prices didn’t go up, even though the price retailers pay to buy in fuel went down.
“There’s no doubt that drivers are getting an incredibly raw deal at the pumps at a time when the cost-of-living crisis is being felt ever more acutely.”
Average fuel prices have increased by around 27p per litre for petrol and 21p per litre for diesel since now-former chancellor Rishi Sunak implemented a 5p cut in duty in March.
Mr Williams went on: “The silence from the Treasury when it comes to supporting drivers through this time of record high pump prices is, frankly, deafening.
“Perhaps it has something do with the fact that it’s benefiting significantly from the increased VAT revenue caused by the high prices.
“We badly need the government to go beyond just vague words and instead actually implement a clear package of financial support to show they’re on the side of drivers.”
Twelve people were arrested on Monday after protesters used “rolling roadblocks” to bring parts of the M4 to a standstill in a demonstration over high fuel prices.
