The firm has apologised for the comment.
An executive at energy firm E.On has sparked anger after saying that the continued high gas and electricity prices would mean "more money for us".
Mark Owen-Lloyd made the comment during a presentation at a seminar run by energy regulator Ofgem looking at the impact of a cold winter on fuel bills.
The firm, which made £877m profit last year apologised unreservedly and said it was investigating.
Prime Minister Gordon Brown said the comments were "inappropriate."
"I think everybody is against people making remarks like that, and I'm pleased that there has now been a full and comprehensive apology," Mr Brown added.
Labour MP Roger Godsiff said the gaffe showed the firm's "contempt" for customers.
Mr Godsiff has been a leading proponent in calling on the Prime Minister to issue a windfall tax on major energy companies.
"It was a very cynical comment that merely shows the contempt that major energy companies have for the general public," he said.
"The really sad thing is, the joke is true and that's why we need the windfall tax."
Asked how high gas and oil prices could be affected by a harsh winter, Mr Owen-Lloyd, the firm's lead power and carbon trader, quipped: "It will make more money for us."
But environment secretary Hilary Benn said that Mr Owen-Lloyd's comment was "not funny" and it was right that the firm had apologised.
"It's tough for people and everybody's got to make a contribution and help and that includes the energy companies," Mr Benn said.
In a statement E.on said: "We apologise unreservedly for the comment that was clearly thoroughly inappropriate.
"We completely understand, and have great concern for, the difficulties facing UK consumers in terms of high energy bills and wish to stress that in no way is this the company's view of the very serious issue of fuel poverty.
"We have now launched an investigation into the context of the comment."