Gas prices to rocket by 15%, millions of families warned

The company, which is the UK’s biggest energy supplier, said it was also facing increased transport and other costs, which could add £50 a year to average bills. If the 15 per cent increase is passed on to consumers, it could mean a £128 a year increase, taking average bills to £1,388.

British Gas, which trades as Scottish Gas north of the Border and has 15.9 million residential customers, increased gas bills by 18 per cent and electricity by 16 per cent in August. Yesterday’s price warning was greeted with dismay by industry commentators, who said consumers were already stretched to the limit.

Audrey Gallacher, director of energy at Consumer Focus, said: “Consumers will need clear evidence that price rises are warranted if they are to stomach further increases to their bills.

“People simply don’t know whether what they are asked to pay is fair – the perception is that suppliers are quick to pass on high price rises and slow to pass on small price cuts.

“Much greater transparency on costs, pricing and profits is needed for customers to know whether they’re getting a fair deal.”

She called for the extra revenue the UK government receives from carbon taxes to be used to help the millions of people who are being hit hardest by rising costs.

Tom Lyon, energy expert at uSwitch.com, said: “This is deeply worrying as consumers are still struggling to come to terms with the £224 or 21 per cent increase in bills from the end of 2010 and only enjoyed a £41 or 3.2 per cent reduction at the beginning of this year.

“Any further increases will see even more people seriously struggling to afford their bills. We would urge all suppliers to hold fire for as long as possible and to ensure that if they do move, it is only in response to a sustained upward trend.

“It’s also important that they recognise the impact it will have on their customers.”

Tom Pering, an energy analyst at Inenco, said cost hikes were caused by a combination of issues, including supply security and the increasing cost of government legislation.

He said: “This increased cost will inevitably be passed on to residential and business customers in the form of higher bills.

“However, the big six energy companies are still not doing enough to inform UK households of their cheapest tariffs and helping them reduce bills.”

Centrica’s shares were up 1 per cent after it said it was trading in line with expectations. In its statement, the firm said: “Non-commodity costs – which are largely outside of our control – are expected to add a further £50 to the cost of supplying the average household this year. The trend for retail energy costs therefore remains upwards.”