
Two charities are taking the government to court because they say not enough is being done to tackle high energy bills.
An act passed eight years ago means the government must take measures in England to end fuel poverty by 2016 and for vulnerable groups by 2010.
Help the Aged and Friends of the Earth want a High Court judicial review which they hope will lead to a judge ordering the government to meet its commitment.
An estimated 5m homes in the UK are currently in fuel poverty.
Fuel poverty is classed as when an individual spends at least 10% of their income on gas and electricity.
The legal action by the charities comes as energy regulator Ofgem publishes the findings of a major inquiry into gas and electricity prices.
BBC social affairs correspondent Sue Littlemore says it is widely accepted that the government is expected to miss its own targets.
Help the Aged and Friends of the Earth will argue that the government is breaking the law by not doing everything reasonable to ease the problem.
In a survey of 1,024 retired people conducted for the two charities, 73% said the government was not doing enough to help people with the rising cost of fuel bills.
Friends of the Earth's executive director, Andy Atkins, said: "The government is letting people down by failing on its legal commitment to end the suffering of fuel poverty.
"At the moment, most homes in the UK are simply leaking heat - to solve fuel poverty in the long term, a massive energy efficiency programme is needed.
"This will keep people warm, cut bills and help meet our targets for tackling climate change."
Help The Aged special adviser Mervyn Kohler said the government's annual reports showed that the number of those in fuel poverty had gone up over the past three years.
"We need a new fuel poverty strategy from the government," he said.
"We need it to be much more vigorous and much faster in impacting than it is planned to do at the moment.
"We have got to try to help people who are really in a crisis situation. I don't think the government has actually got the measure of what this crisis really is."