Mary Phillips, a 72-year-old British pensioner, says she often escapes the cold of her council flat and the dread of unaffordable fuel bills by taking refuge in her centrally-heated local library.

But this week, she took her sofa to the streets outside the High Court to try to force the British government to do more for people like her who are being forced into an often fatal choice between heating and eating.

Wearing fluffy boots, wrapped in blankets and a dressing gown, and clutching a hot water bottle to her chest, she posed as a symbol of the some 25,000 elderly people who will die of the cold in Britain this winter.

Data collated by a lobby group, National Energy Action, show that despite a relatively mild climate, 19 per cent more people in England die in winter than in other seasons, compared with 10 per cent in Finland, 11 per cent in Germany and 12 per cent in Denmark.

"Fuel poverty" - a phenomenon that has crept into the lower income brackets of British society in recent years - is now at the top of the political agenda, with energy prices soaring and incomes under pressure as the economy buckles under the credit crunch.

Charities say five million people in Britain will struggle to heat their homes this winter, and this week they took the government to the High Court to explain why it is not doing more to help them.

A household in "fuel poverty" is defined as one that spends 10 per cent or more of its annual income on gas and electricity, and the government has promised to do everything "reasonably practicable" to end it in vulnerable households by 2010.

"It's not all older people, but our estimates are that about one in four people aged 60 and over are living in fuel poverty," said Paul Bates, a spokesman for the Help the Aged charity, which launched the court action with environmental campaign group Friends of the Earth.

"The most vulnerable people in our society are really struggling. The basics of life are prohibitively expensive."

Fuel poverty is unique because it is the only poverty measure that the British government has pledged by law to tackle. Even the eradication of child poverty - one of Prime Minister Gordon Brown's oft-stated aspirations - is not a goal supported by legislation.

The government admits it is struggling to meet its own target - putting it at risk of losing the High Court case and being forced into a judicial review of its policy decisions - but says factors beyond its control are compounding the problem.

"This government is still committed to tackling fuel poverty, but ... sharply rising energy prices have made this goal increasingly difficult," Environment Minister Hilary Benn said in a statement.

According to government figures, the overall cost of energy to domestic consumers rose by 22 per cent in real terms between 2005 and 2006, and prices have jumped yet more dramatically since then with global oil prices reaching record highs.

Ms Benn said the government had spent £20 billion on the problem since 2000 and would continue to urge energy suppliers and insulation firms to help improve energy efficiency in homes.

Gas and electricity suppliers have been sharply criticised in Britain for raking in huge profits and imposing sharp price rises on customers already struggling with inflation rates of more than four per cent on other consumer goods.

The government announced an energy efficiency package in September which included £910 million of extra cash from the utilities to help householders facing soaring bills to make their homes more energy-efficient.

But for Mary Phillips, the government's promises and pledges are not enough. Her sums still don't add up.

Living alone on a council estate in southeast London, she has an income of £148 per week. On top of housing service charges of £7.30 per week, her weekly gas bill is £9 and her electricity costs more than £4, but she is still reduced to shivering at home or finding refuge in warmer public buildings.

"Every day I have to think if I can possibly afford to put the heating on," she said in an interview.

"I always wear extra clothes, and I try never to put the heating on in the middle of the day, and at night I wear a bed jacket and bed socks rather than have the heating on.

"I often go to the local library and sit in there, because it's warmer, and I also have a hot water bottle which I use as an extra source of heat."

Campaigners say proof that government action is inadequate lies in a grim set of figures released by the Office for National Statistics each year detailing a phenomenon called "excess winter deaths" - the number of older (over 60s) people who die from cold-related illness in the winter.

Over the past decade, it has averaged around 25,000 - a figure that remained high throughout the economic boom that preceded the recent downturn, and has failed to budge despite headline-grabbing government initiatives such as one-off winter fuel payments to the elderly and a £74 million "Warm Front" scheme to improve home insulation.

And, campaigners point out, it is a statistic which is all the more telling because Britain's winter temperatures are relatively kind compared with those of northerly neighbours.

"It is totally unacceptable," said Mr Bates. "People should not be dying of the cold in this day and age in a country as rich as the UK. It's not even very cold here. If you look at places like Scandinavia where the weather is much colder, the concept of excess winter deaths is virtually unheard of."

Fuel poverty in Britain

A household is deemed to be in "fuel poverty" when it needs to spend more than 10 per cent of its income on fuel in order to heat its home to an adequate temperature.

• The Labour government introduced legislation in 2000, the Warm Homes and Energy Conservation Act, which stated its intention to do everything "reasonably practicable" to end fuel poverty in vulnerable households by 2010 and in all households by 2016.

• Campaigners for the elderly and for the environment estimate that in 2008 there are at least five million households in fuel poverty across Britain.

• Some 25,000 people die in Britain each year from cold-related illnesses, according to the Office for National Statistics.

• The government says it has spent some £20 billion on tackling fuel poverty since 2000.

• Latest government figures show there were 3.5 million households living in fuel poverty in 2006, an increase of one million since 2005.

• Lawyers acting for the government in the High Court said that dramatic increases in energy prices - a factor which they said was "outside the government's direct control" - have caused "a significant rise in numbers of households in fuel poverty" in recent years.