Around 8.5 million households are being hit with a 6% rise in their energy bills as British Gas becomes the latest utility giant to hike its tariffs.
The move is estimated to add another £80 to the typical annual dual-fuel bill for a British Gas customer, or £1.50 a week.
The price increase is more than double the rate of inflation.
It was first announced last month but has sparked renewed anger after British Gas parent company Centrica revealed it was set to make profits of £1.4bn this year.
Experts also predict around £575m of pre-tax profit from its British Gas residential arm after gas consumption for the first 10 months of 2012 rose 9% because of colder than normal weather.