Centrica, which operates British Gas, said in a statement that they have found no "cause for concern" in gas trades they have reviewed:
Centrica participates actively in the UK wholesale gas market in order to meet our commitments to our customers.
We trade in the wholesale gas market every day. In this respect, 28 September 2012 was no different.
We have reviewed all our trades executed around the close of the market on that day and have found nothing unusual about them or any cause for concern.
A former energy trader has told ITV News the electricity market has been rigged and it is "worse" than the gas market.
Another market, another investigation. The Energy and City watchdogs start investigations into allegations of traders fixing the gas price.