Sharp increases in energy costs will effect the district's most vulnerable and will lead to a rise in the number of winter deaths, Bradford's Age Concern has warned.

Keith Nathan, the chief officer at Bradford and district Age Concern, said elderly people would be most at risk by the rises which are about four times the rate of inflation.

Npower was the latest on a list of energy suppliers to announce an increase in both gas and electricity charges.

Despite threats of a colder than usual winter the company plan to increase the cost of gas bills by 13.7 per cent and electricity bills by 12 per cent in January 2006.

Mr Nathan said 25,000 people across the UK died last year because of the cold. "Anything that's going to make elderly people more likely to turn off the fire, or not even put it on, is going to add to that," he said. He said the price increases seemed steep when matched against the cost of inflation.

"It's these kinds of pressures adding to the danger that people won't feel they are able to keep warm, it adds to the stress of life," he said.

Sue Adsetts, of the Gingerbread Centre, a single parent support group, warned families on low incomes would also be hit hard by the price hikes. "It's just another nail in the coffin of not helping people," she said.

And she said those who paid their energy costs with a top-up card, rather than through regular instalments would be left out in the cold.

"Ninety per cent of the people that we deal with, pay for their utilities with a card system. People who use these cards pay a higher rate," she said.

Karl Brookes, a spokesman for watchdog Energywatch, said it the most vulnerable customers were already using the more expensive card system and they were most likely to self-disconnect.

"They have put up their prices literally in the middle of the bleak mid-winter," said Mr Brookes. "People get worried about the price increase and opt to sit there in the cold and the dark, they self-disconnect."

Mr Brookes also warned the increases would plunge thousands of households into fuel debt and he urged customers to shop around.

npower's proposed changes came with a promise to help vulnerable customers with a price plan. Mr Brookes said it was important that npower make those vulnerable customers aware of their eligibility to enrol on such schemes.

"That scheme needs to be promoted properly and we trust npower to do that," he said.