Consumer Focus says firms appear to be raising prices 'with impunity'
Energy prices in the UK have increased twice as fast as the European Union average, according to latest figures.
Organisation for Economic Co-operation and Development statistics showed gas and electricity bills rose 29.7% in the past year compared with 15% in the EU.
Government watchdog Consumer Focus said UK customers were being hit "faster and harder" than those in Europe.
The UK's Energy Retail Association said prices had become more vulnerable to fluctuations across the world.
The OECD figures also showed prices for customers were up by 12.2% in Germany and 14% in France.
Consumer Focus chief executive Ed Mayo said the UK should learn from other countries which may be doing more to keep their prices down.
"The UK has a relatively free market, but the freedom to cut prices in the early years now seems to be the freedom to raise prices with impunity," he said.
"Of course, those least able to afford it suffer most. The suppliers must offer their most vulnerable customers social tariffs and reduce prices generally at the earliest opportunity."
The latest figures from regulator Ofgem suggest British gas bills are the cheapest in Europe, and electricity bills are at similar levels to the rest of the continent.
However, this does not take account of price rises which have taken place so far this year.
A spokesman for the Energy Retail Association said: "What the OECD's figures fail to demonstrate is that British customers have enjoyed historically very low prices compared to Europe and indeed the rest of the world.
"Primarily, this is due to us having our own vast reserves of natural gas in the North Sea and not being exposed to global prices in the same way as we are now.
"We are no longer an energy island. With increased demand from growing economies such as India and China, the prices we now pay for our energy are more vulnerable to fluctuations across the world."
Children's charity Barnados called for mandatory social tariffs to be introduced and for pre-paid meters to be made fairer.
Chief executive Martin Narey said: "It is an embarrassment that children in the fifth richest country in the world are suffering the consequences of irresponsible rises in fuel costs - almost double the increase seen by our European counterparts.
"The government is overlooking the plight of children and families - most of who, with the effects of rising fuels bills, are facing their hardest winter ever. Something really must be done now, the alternative is bleak."