Diesel drivers who are filling up before the end of May have been warned prices are rising - and they could be being OVERCHARGED. Diesel drivers in the UK heading to petrol forecourts up and down the country have been warned over a "glaring" problem by the RAC.

New RAC figures show diesel rose by 2p to 157.76p, taking a 55-litre tank of diesel to £86.77 (up £1.10 in April). The RAC warned: "Those driving diesel vehicles not being consistently overcharged. This is a regular occurrence borne from retailers upping margins on diesel to subsidise the price of petrol."

Diesel prices at Asda show a 155.5p average, while Morrisons is 155.7p and Sainsbury's and Tesco 153.8p and 154.4p respectively. Minimum prices at Asda, Morrisons, Sainsbury's and Tesco stores are 147.7pm 148.7p, 144.9p and 148.9p.

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The max prices are 183.9p, 161.9p, 160.9p and 156.9p respectively - meaning Asda, Morrisons, Sainsbury's and Tesco have 36p, 13p, 16p and 8p differences. The difference between BP’s cheapest and most expensive diesel was a shocking 30p while for Shell it was 28p.

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."

He added: “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. To put this into perspective, the wholesale price of diesel has been lower than petrol since the middle of April, yet diesel is nearly 8p a litre dearer at the pump. If retailers were treating drivers fairly this gap would be starting to close, instead of getting wider."

He went on: “This has prompted the RAC to call on the Government and the Competition and Markets Authority (CMA) to get to grips with unfair retailer margins once and for all via the imminent ‘Pump Watch’ scheme and the creation of a price monitoring body. Worryingly though, 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."