Motorists were hit by a record monthly hike in petrol prices in June.
RAC analysis shows the average cost of a litre of the fuel at UK forecourts rose by 16.6p last month, from 174.8p to 191.4p.
That is the highest monthly increase in records dating back to 2000.
The surge in prices added more than £9 to the cost of filling a typical 55-litre family petrol car.
Average diesel prices rose by 15.6p per litre, ending the month at 199.1p.
The RAC said 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.
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 Chancellor Rishi Sunak implemented a 5p cut in duty in March, leading to calls for the Government to take further action.
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 as dozens of campaigners calling for another cut in duty targeted the M4 in South Wales and Somerset, and stretches of the M5 from Devon to Bristol, with rolling go-slow roadblocks in the morning rush-hour.
Home Secretary Priti Patel called on police to use new powers which include imprisonment to stop fuel protesters bringing gridlock to major roads.
Labour’s shadow transport secretary Louise Haigh said: “This hapless Conservative Government is so mired in scandal and chaos that it has no answers to the savage price hikes facing working people during a cost-of-living crisis.
“The Tories need to act urgently and tackle the profiteering of petrol giants, and ensure retailers pass on fuel duty cuts to consumers, to put money back in people’s pockets.”