The government is taking allegations that wholesale gas prices have been manipulated "very seriously", Energy Secretary Ed Davey has told MPs.
In a Commons statement on 13 November 2012, Mr Davey said: "I see it as my job to protect consumers, not least the most vulnerable who can suffer the most when markets are abused."
The Financial Services Authority (FSA) and energy regulator Ofgem are investigating claims that the wholesale price of gas has been artificially lowered.
All of the UK's big six energy suppliers have released statements denying any involvement.
"Firm action" would ensue if the claims proved to be true, he added.
It was not possible to understand what impact any attempted manipulation would have had on prices paid by consumers, the energy secretary said.
Shadow energy secretary Caroline Flint said: "Energy companies are very quick to blame wholesale costs when they put up people's bills, so any suggestion that the wholesale gas market has been manipulated is a very serious allegation that needs a full and rapid investigation."
She repeated Labour calls for Ofgem to be scrapped and replaced with "a tough new regulator".
"The allegations that have been made in the last 24 hours suggest there are deep, structural problems with the way our market works and is regulated," she told MPs.