Six million households face a shock next month when an average fuel bill of £530 pops through the letterbox, experts warned yesterday.
The bill – the biggest ever single payment demanded by the energy giants – will hit the quarter of the country's customers who pay for their gas and electricity four times a year.
The £530 figure is £50 higher than the average winter quarter bill last year, following a spate of winter price rises. All the Bix Six energy firms increased the cost of their tariffs at the end of last year.
The record bills are likely to make even more customers struggle to light and heat their homes.
An analysis by Moneysupermarket website released yesterday showed that half of a household's gas consumption, 45 per cent, occurs between 13 November and 15 February.
A third of a home's annual total electricity is consumed during the same period, meaning that 39.4 per cent of a household's annual use falls within just three months.
As a result, the website calculated that the bill for those winter months would hit £530, which it said would be "a substantial blow to any household after the expense of the festive season".
"Many households will be dealing with a festive financial hangover this January so a huge energy bill will come as an unwelcome shock," said its consumer finance expert Clare Francis.
"A spate of price rises which mostly came into effect before the Christmas period saw the cost of energy increase by an average of 7.6 per cent, leaving many people worrying about the crippling costs they could face in the coming month."
Average annual fuel bills are now £1,343, compared with £1,250 last year. An estimated 6.5 million households have been left in fuel poverty this winter because of the hikes which have increased the average annual bill to £1,343.
Energy UK, which represents suppliers, acknowledged the next quarterly bill would concern some customers. Angela Knight, its chief executive, said: "With the current state of the economy, we know that people will be worried about their household bills after Christmas.