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."
Regulators have called for an investigation into the UK's Big Six energy suppliers amid soaring household bills and rocketing profits.
Ofgem's finding that aspects of energy firms' behaviour "would appear to be consistent with tacit coordination" has been denied by Centrica.
The inquiry into the 'Big Six' energy firms is a significant moment, but don't hold your breath, it will take the best part of two years.