
Millions of UK homes are facing higher gas and electricity bills as the latest price increases from British Gas have come into effect.
British Gas owner Centrica first announced the rises in July, with gas bills up by 12.4% and electricity bills rising 9.4%.
The firm has blamed the move, its second set of price rises this year, on continuing high wholesale energy costs.
Rival energy providers have also increased their bills this year.
According to watchdog Energywatch, following the 4 September price hike, British Gas is now the most expensive energy firm in the UK.
The company's average annual gas bills having increased by 91% since 2003, and its electricity bills having risen 81% over the same period, Energywatch said.
The latest price rises at British Gas come after it reported record losses of £143m for the first six months of this year.
It last increased costs for its 16.5 million customers by 22% in March.
Energywatch, along with charities Help the Aged and Child Action Poverty Group, warned that old people as well as the disabled are set to be the most affected by the higher gas and electricity prices.
As frequent users of prepaid meters, they are being charged even more than those billed on a quarterly basis, the organisations said.
Meter customers are being charged as much as £173 more for their gas, and their electricity bills are as much as £113 higher annually, the groups claimed.
The coalition is calling on the six largest energy companies, including British Gas, to set the rates for prepaid meters at the same level as those for consumers who are sent quarterly bills.
The price of wholesale gas in the UK have been increasing as the country's stocks in the North Sea have declined, forcing more to be imported from Europe.
Wholesale gas and energy prices have also risen in line with the high cost of oil, which has increased because of political instability in the Middle East and strong global demand led by fast-growing economies such as China.