Scottish and Southern Energy (SSE), Britain's second-biggest energy supplier, is increasing its tariffs by an inflation-busting 15.8 per cent.

Customers switching to SSE will pay higher tariffs from today and bills for the company's 8.5 million existing customers will rise from April 1. Prices for electricity customers will increase by an average of 14.2 per cent and prices for gas customers will increase by 15.8 per cent. The move came as forecasters were predicting Arctic weather this weekend.

SSE is the last of the six leading energy companies to increase its prices this year. In January it pledged to keep rates unchanged until March 30. Scott Byrom, of moneysupermarket.com, the price comparison website, said: “It is a little disappointing it has only managed to hang on for another 48 hours.”

An SSE executive apologised for the move. Alistair Phillips-Davies, the energy supply director, said: “Wholesale energy prices have been stubbornly high. You cannot resist indefinitely the impact of these issues and I am sorry that all of this has culminated in the price rises we are announcing today.”

The price rises come amid an investigation by Ofgem, the energy regulator, into electricity and gas suppliers after several big players announced both double-digit price rises and bumper profits. Centrica, the owner of British Gas, reported record annual profits of £1.9 billion in February, only a month after it had raised prices by 15 per cent.

The energy companies say that rising wholesale costs have forced them to increase prices. Experts say that SSE's price rises will push the average energy bill for the customers of all six big energy firms to more than £1,000 a year. This will pile more pressure on homeowners, who are having to cope with spiralling mortgage, water and council tax bills.

It emerged yesterday that the increases in energy costs have pushed inflation up to 2.5 per cent from 2.2 per cent last month, above the Bank of England's target rate of 2 per cent. More than 2.25 million pensioners struggle to keep warm in colder months because of expensive energy bills, according to recent research from Age Concern, the charity.

Frances Walker, of the Consumer Credit Counselling Service, a debt charity, said: “It's getting harder and harder for people to meet their everyday living costs.”

Tim Wolfenden, of uSwitch.com, the price comparison website, said: “SSE have managed to delay their price until after most of the cold weather, which will have been welcomed by their customers. But the question is now, are there more price rises on the horizon later this year?”

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