Fears that more households will be plunged into a "long, cold winter" have been fuelled after two major energy companies hiked their prices.

British Gas put an extra £80 on to its typical annual dual fuel bill after an average increase of 6% affecting 8.5 million customers from November 16. Rival npower followed with an average rise of 8.8% for gas and 9.1% for electricity.

Both companies blamed rising costs largely outside their control, but with food and some mortgage costs also on an upward path there were fears about how the elderly and hard-up will cope with the latest rises.

The pre-winter move from British Gas comes months after parent Centrica posted a 23% rise in half-year profits at its residential arm to £345 million. Unions and consumer groups attacked British Gas and called on the Government to take urgent action to tackle rising fuel prices.

Unite general secretary Len McCluskey said: "With winter approaching, low-waged people will now be terrified about how they are going to find another £80. Money from the poor is going to the pockets of Centrica shareholders. This is further shameful abuse by out-of-control, greedy fuel companies, sitting on piles of profit."

Consumer Focus recently said six million households in England were planning to cut back on their heating this winter because of cost worries. It has encouraged customers "to do what they can" to cut their bills by switching tariff, payment method and supplier.

Its director of energy Audrey Gallacher said no-one has managed to convince consumers of the necessity for price rises in the context of wholesale prices and company profits. She added: "We need much more focus on the big steps that Government and the regulator can take to insulate consumers from the effects of growing energy costs."

Consumer Focus said the price price rise from British Gas will see the company's average annual energy bills reach almost £1,265 for direct debit customers and £1,347 for cash and cheque customers.

The rise from npower comes into force on November 26 and according to Consumer Focus will result in a typical dual fuel customer paying £1,252 by monthly direct debit. The figure for cash or cheque is £1,357. The supplier has 6.5 million residential gas and electricity accounts.

SSE, which trades as Southern Electric, Swalec and Scottish Hydro, has already said it will increase tariffs by 9% on average on Monday, hitting about five million electricity customers and 3.4 million gas customers.