Consumer groups called for immediate cuts in energy bills today following the announcement that British Gas profits had jumped 58%.
Philip Cullum, deputy chief executive of Consumer Focus, said there are "no excuses" for not reducing tariffs and claimed the market is in need of "fundamental reform".
The GMB union said the Government should intervene to help those struggling to pay.
The calls came after Centrica revealed its British Gas residential arm made profits of £595 million last year - up 58% on 2008.
Mr Cullum said: "Energy companies have no excuses for not cutting bills for their customers. It is clear the problems in the energy market are profound and that it requires fundamental reform.
"For consumers, a combination of high prices and cold weather has exacted a heavy cost.
"Energy companies have taken advantage this winter, while more than six million UK households live in fuel poverty and face a desperate struggle to keep warm.
"That British Gas has been the only major energy supplier to cut standard prices over the past seven months demonstrates a market largely devoid of competitive pressure. Energy companies seem not to care about providing value for money."
Mr Cullum said the market is "crying out" for greater transparency.
"Unlike the other members of the big six, British Gas reports its results in detail and so takes much of the flak that deserves to be shared with the other companies.
"If ever a market was crying out for greater transparency, it is the current UK energy market.
"Our big energy companies are producers and generators as well as retailers. As producers they do very well when wholesale costs are high, as retailers they do very well when wholesale costs are low. It really is a case of heads they win, tails we lose."
Gary Smith, GMB national secretary for energy, said: "GMB is asking the Government to look at redirecting some of these excessive profits back to the most vulnerable and needy energy users in our society. There should be lower tariffs for these consumers."
Simon Hughes, Liberal Democrat energy spokesman, said: "These massive profits show that the energy companies are out of control and their regulator is out of action.
"The six big beasts of the energy jungle must be tamed immediately - to stop their predatory activities which are so dangerous to the public.
"Liberal Democrats will change the rules so that fuel bills reflect fuel costs and consumers are not ripped off again and again."Reuse content