Fleet operators running diesel vehicles are being overcharged by nearly 5p per litre, hitting businesses firmly in the back pocket, according to the AA. Following an analysis of wholesale price data from the European Union (EU) on at least three occasions in 2012 the value of petrol spiked across north-western Europe to the same level as diesel. In the spring, diesel was in fact the same price or cheaper than petrol for almost an entire month. UK wholesale prices given to the AA showed that between March 21 and April 18 this year, diesel prices ranged from the same prices as petrol to as much as 2p per litre cheaper. The price gap appears to be closing again at present, while fleets continue to pay a premium for diesel on the nation's forecourts. Current fuel price data indicates the average price of diesel in the UK was 143.11p per litre last week, while petrol was 4.8p per litre cheaper at 138.33p. The claims of overcharging for diesel fleets come just weeks after the Office of Fair Trading (OFT) set the wheels in motion regarding its own preliminary investigation into the equality of petrol and diesel markets. The Government has also responded insisting it will investigate the issues surrounding accusations of oil traders and speculators allegedly rigging markets to drive up the price of fuel for fleets. Edmund King, president of the AA, said: "If the EU can publish a weekly track of petrol and diesel wholesale prices in euros per tonne, why can't the UK Government publish an equivalent in pounds per tonne or pence per litre on one of its websites? "It doesn't need an investigation, or permission from fuel retailers or suppliers, just a form that can be understood by the public and businesses to ensure a fair price for all parties." Industry figures suggest up to 80 per cent of UK fleets run with diesel vehicles, but some operators are being forced to consider switching to petrol vehicles, particularly with manufacturers now working harder than ever to reduce CO2 emissions from petrol cars.