Petrol and diesel prices could jump 2p a litre because of the ongoing rogue petrol fiasco, drivers were warned last night.

The Sunday Mirror reports that the rise will happen because supermarkets will have to pay higher prices for emergency replacement stocks. The price hike warning came as the contaminated unleaded petrol blamed for thousands of cars breaking down was traced to four storage tanks at a depot in Thurrock, Essex.

Angry motoring groups immediately accused oil companies and suppliers of profiteering. An RAC spokesman said: "It's wrong and it will be totally counterproductive. This will backfire on the supermarkets and garages who sold this contaminated fuel in the first place".

The AA added: "Motorists are being penalised for someone else's mistake".

Harvest Energy, who supply store chain Asda and other petrol retailers from the Royal Vopak terminal on the Thames Estuary, said tests had found "unusually high levels" of silicon in the tanks. The depot also stores fuel for oil company Greenergy, which supplies Tesco and Morrisons.

One theory under investigation last night was that the silicon - used in diesel to stop the fuel frothing up when drivers fill up at garages - had been put into the wrong storage tanks.