A campaign for an investigation into fuel price manipulation is being backed by a Westcountry MP.
A 30,000-signature petition has now been handed to the Office of Fair Trading (OFT) calling for a full inquiry into soaring pump prices.
It follows allegations in May that BP and Shell had inflated oil prices – claims that are now being investigated by the EU.
North Cornwall Liberal Democrat MP Dan Rogerson also wants the OFT to intervene and has backed the petition organised by the campaign group Fair Fuel UK.
"Time and time again, local people and businesses tell me that the cost of petrol and diesel is one of their biggest concerns," Mr Rogerson said.
"That's why I am making it one of my priorities to do everything I can to keep fuel prices down to help local people with the cost of living – including by campaigning for the 5p-a-litre reduction in tax on fuel to be extended to rural North Cornwall.
"But it is important to explore all the options – we have heard allegations in recent years from whistleblowers that the oil industry actively engages in Libor-like oil price manipulation. It is about time that these rumours were fully investigated by the OFT so that we can get to the bottom of what is going on.
"With investigations under way in America and Europe, I am calling on the OFT to do the same. The coalition Government has acted to freeze fuel duty since 2010, but if oil companies are manipulating oil prices, all of our hard work could be going to waste."
The OFT did little to relieve the pressure on rural motorists earlier this year when its report on the fuel sector found pump prices were 2p a litre more expensive in the countryside but concluded the market was "working well".
It put the rise in costs over the past ten years down to increases in tax and the cost of crude oil.
It said there was "very limited evidence" that retailers quickly hiked prices when the wholesale price rose, but let them fall more when it dropped. Further investigation was ruled out.
The OFT did recognise that competition in areas like the Westcountry was weaker and found petrol was around 1.9p a litre more expensive and diesel around 1.7p a litre more expensive in rural areas than in urban areas.
Fewer competitors, higher transport costs for getting fuel to rural forecourts and lower throughputs were to blame, according to the official report.
Calls for a fresh inquiry into the fuel sector came as the AA warned that prices of petrol and diesel could rise by 5p a litre because of market speculators. It warned that would cost a family travelling from London to Cornwall an additional £2.90 in fuel. In all, the AA said, that could strip some £250,000 away from the tourism business into the pockets of the fuel industry.
