The number of UK households living in fuel poverty has risen by 83%, or 1.7 million, since 2004.
Too many elderly will still have trouble paying their heating bills
The government admits the situation has become worse because of the sharp increases in the price of gas and electricity in the last two years.
The fuel-poor are those who spend at least 10% of their income on heating.
The figures are published by the government in its fourth annual progress report on its strategy to alleviate fuel poverty.
The number of UK households defined as "fuel-poor" in 2004 was about two million, the same as in 2003.
But that figure has now shot up.
For the UK as a whole the estimated increase has been from two million to nearly 3.7 million in 2006.
In England the number of homes where people spent more than 10% of their income on heating has gone up from 1.2 million to 2.2 million.
The charity Help the Aged said it was very disappointed.
"The latest figures show that the targets for reductions of fuel poverty by 2010 are in jeopardy, which should sound the loudest of alarm bells among ministers," said spokesperson Anna Pearson.
"The government must redouble its efforts or vulnerable older people face yet another cold and difficult winter ahead, with probable rises in the numbers of excess winter deaths."
The government now admits it will miss its target of eliminating the number of English households in fuel poverty who it regards as most vulnerable - those containing children, the elderly, sick or disabled.
It thinks in 2010 there will still be 1.2 million of them, and possibly as many as 2.1 million.