Media playback is unsupported on your device Media caption Ed Davey says the government is "deeply concerned"

David Cameron is extremely concerned by claims of price fixing by major oil companies, Downing Street has said.

The prime minister's spokesman said it was "deeply worrying" if prices have been driven up for consumers.

Oil giants including BP and Shell are facing claims they have been fixing prices for more than a decade.

It follows a raid on the offices of BP, Royal Dutch Shell, and Norway's Statoil by European anti-trust regulators.

The companies said they were co-operating with investigators.

In a Commons statement, Energy Secretary Ed Davey said the Office of Fair Trading (OFT) was working with European Commission investigators but stressed their inquiries were at a very early stage and urged MPs not to "jump the gun".

'Limp-wristed'

But he promised the "full force of the law" would be brought down on the companies if the allegations were found to be true.

We expect the companies concerned to fully comply with these investigations Ed Davey, Energy Secretary Q&A: Why are fuel prices rising?

"This government is deeply concerned by any allegation that prices for consumers could have been artificially or unnecessarily driven up," the Lib Dem cabinet minister told MPs.

"The UK government and regulators will provide any assistance necessary to the European investigators and we expect the companies concerned to fully comply with these investigations."

He also defended the Office of Fair trading which found no evidence of price fixing when it carried out its own investigation into the petrol market last year.

Tory MP Robert Halfon, who has been campaigning for cuts to fuel duty and greater transparency, attacked the OFT's inquiry as "limp-wristed and lettuce-like".

Despite calls for a full probe into petrol pricing, amid claims of price fixing by a whistleblower, the regulator had failed to spot any of the allegations now being investigated by the EU, said Mr Halfon.

'Shocking behaviour'

He called on the government to change the law so that people could be jailed "for fixing oil prices" and for any cash recovered in fines, if the companies are found guilty, to be returned to motorists.

Caroline Flint, responding for Labour, said the allegations "if true" were an example of "shocking behaviour in the oil market which should be dealt with strongly".

She called on the OFT to re-open its investigation into the petrol market.

Mr Davey said the OFT was an "independent body, a strong body", which has powers to determine its own investigations and the government could not interfere.

He rejected accusations of complacency from some MPs, saying the government had tightened up competition laws.

European Commission officials said its investigators made the "unannounced inspections" on Tuesday amid concerns that "the companies may have colluded in reporting distorted prices".

It did not name the firms, and emphasised that the raids did not mean the companies were guilty of any charges.

'Huge impact'

But BP, Shell, and Statoil, and also the oil pricing agency Platts, confirmed that they were working with the authorities in their inquiries.

In a statement the European Commission said: "Even small distortions of assessed prices may have a huge impact on the prices of crude oil, refined oil products and biofuels purchases and sales, potentially harming final consumers,'"

As part of the investigation, the Commission said it was examining whether the companies may have prevented others from participating in the pricing process "with a view to distorting published prices".

It added: "Any such behaviour, if established, may amount to violations of European antitrust rules that prohibit cartels and restrictive business practices and abuses of a dominant market position."