The chief executive of Centrica, which owns British Gas, has welcomed the major competition inquiry into energy firms but said a lengthy review could damage investment when the market's "security is being seriously challenged."
Sam Laidlaw said: "Anything that clears the air and helps rebuild trust in the industry must be a good thing. Britain's energy market is highly competitive and we believe that a full independent review by a respected regulatory authority would demonstrate precisely that.
"Competition is working, providing choice for consumers and some of the lowest prices in Europe.
"We hope that a lengthy review process will not damage confidence in the market, when over £100 billion of investment in new infrastructure is needed.
"A prolonged period of uncertainty could damage investment at a time when Britain's energy security is being seriously challenged."