Average petrol and diesel prices have risen by 10p per litre so far this year, new figures show.
The RAC said the average price of a litre of petrol increased by 3p to 150.0p in April alone.
It claimed drivers are being “seriously overcharged for diesel”, with average prices rising by 2p per litre to 157.8p in April.
Rising pump prices since the start of the year have added around £5.50 to the cost of filling a typical 55-litre family car.
The RAC is calling on the Competition and Markets Authority (CMA) – an independent non-ministerial Government department – to address “glaring issues” with fuel retailing.
It wants the regulator – which is responsible for monitoring prices and will oversee the incoming PumpWatch price transparency scheme – to tackle “unfair retailer margins which lead to drivers getting a raw deal”.
The RAC said if the biggest fuel retailers charged “fairer margins” it would benefit drivers in several ways, such as:
– Ending the “postcode lottery” which means some companies charge “wildly different prices” across locations.
– Stop so-called rocket and feather pricing, where pump prices surge when wholesale costs rise, but fall slowly when wholesale costs decline.
– Reduce fuel prices in Britain to levels in Northern Ireland, where they are consistently 5p per litre cheaper.
Despite the CMA expressing concern about retailer margins earlier this year, the average margins for a litre of petrol and diesel is 9.5p and 17.5p respectively, according to the RAC.
The long-term average margin for both fuels is around 8.0p.
RAC fuel spokesman Simon Williams said: “Drivers are once again having to dig deep just to go about their daily lives.
“Our data shows petrol and diesel have now gone up 10p a litre so far this year on the back of further increases in April of 3p and 2p respectively.
“Some of this is down to the oil price and the pound-to-dollar exchange rate making wholesale petrol more expensive for retailers to buy.
“But unfortunately, it’s also very apparent that retailers are making massive margins on diesel.
“Worryingly, the CMA’s warning shot about higher retailer margins at the end of March appears to have fallen on deaf ears, meaning drivers are once again being seriously overcharged for diesel.”