Some cash-strapped British pensioners are buying books from charity shops and burn them to keep warm as freezing temperatures gripped the UK, a London newspaper reported Tuesday.

Workers at a charity shop in Swansea, in south Wales, told London newspaper Metro that pensioners were looking for thick books such as encyclopedias — which are sold for a few pennies second hand — as a cheaper alternative to coal.

"Book-burning seems terribly wrong but we have to get rid of unsold stock for pennies and some of the pensioners say the books make ideal slow-burning fuel for fires and stoves," the paper quoted one shop assistant as saying.

"A lot of them buy up large hardback volumes so they can stick them in the fire to last all night."

Energy prices have soared in Britain in the past years, with some estimates showing gas prices up by around 40 percent since January 2008, and electricity tariffs rising by about 20 percent.

Britain's National Grid, which is responsible for the country's energy needs, issued an alert Monday that consumption may have to be cut if supplies of gas do not improve soon.

Gas is used to heat about two thirds of British homes and consumption surged to 30 percent above the seasonal average Monday.

"The spiraling cost of energy means heating homes has become a luxury rather than a necessity for many people – particularly the elderly, low paid and unemployed," Ruth Davison, director of campaigns and neighborhoods at the National Housing Federation, told the paper.