The RAC has said supermarket petrol prices may no longer be the cheapest and advised motorists to “shop around”.
The roadside recovery firm warned major retailers were failing to reduce petrol prices in line with falling wholesale costs.
Fuel prices hit their highest-ever levels earlier this summer as the UK’s cost-of-living crisis began to bite.
RAC fuel spokesman Simon Williams advised drivers to no longer assume supermarkets had the lowest fuel prices.
He said motorists should “shop around as it’s highly likely you’ll find an independent retailer which is doing the right thing and fairly reflecting their lower wholesale costs by charging a lower price”.
Watch: Supermarkets are failing to reduce petrol prices in line with falling wholesale costs, RAC says
The “big four” supermarkets – Tesco, Asda, Morrisons and Sainsbury’s, along with several other suppliers – have faced criticism for failing to reduce their prices in line with falling wholesale costs.
According to the RAC, the wholesale cost of petrol has fallen by 20p since early June.
Yet UK retailers continued to increase their prices in June and only dropped their pump prices by an average of 9p during July, the organisation said.
This meant drivers filling up at the end of July at an average of 183p per litre could be paying almost £9 a tank more than they should be.
Equally, the RAC said motorists should now be paying about 182p per litre for diesel – nearly £6 a tank less than the end of July average of 192p per litre.
Williams added: “July has been an unnecessarily tough month for drivers due to the big four supermarkets’ unwillingness to cut their prices to a more reasonable level, reflecting the consistent and significant reductions in the wholesale cost of petrol and diesel.
“As it was, we saw independent retailers leading the charge, with fairer pump prices appearing all around the country, which eventually forced the supermarkets to finally implement a more substantial cut late last Friday afternoon.
“What ought to have happened is that the biggest retailers cut their prices more significantly on a daily basis, given the wholesale price of petrol has fallen steadily over the last eight weeks.”
AA president Edmund King also criticised major retailers for failing to drop prices, branding it “unforgivable”.
How to find cheap petrol near you
Price comparison website PetrolPrices finds the cheapest petrol prices all across the country.
It gets some of its information from special analysts, but it also collects information from its users who report the price of petrol.
You have to make an account to access its website or app, but once in you can search by city or postcode for the cheapest prices near you.
Confused.com also provides a similar service where you just need to enter your postcode for them to present the cheapest prices near you.
You can search once a day without an account or unlimited times with an account.