Centrica, the owner of British Gas, has warned that the intense political debate over gas and electricity prices has put Britain at risk of blackouts as soon as next year.

Rick Haythornthwaite, Centrica's new chairman, said threats to impose price caps or break up Britain's biggest energy supplier was raising the real possibility of "the lights going out in Britain".

He said: "I think the reputation of Britain as a place in which to invest is under threat and the time to correct that is now, not after the 2015 election, by which time the possibility of the lights going out in Britain will be looming much larger. I don't see this as the figment of a scaremonger's imagination. I think right now we've got to restart collaborative, constructive dialogue around these key issues; we cannot afford to wait, hostilities have got to cease."

Experts have warned that the gap between energy supply and demand is close to crisis levels as the UK has not been quick enough to build new power stations as old coal plants are closed down. Sir John Armitt, who is also advising Labour on Britain's infrastructure, has warned that the country's energy capacity surplus is down to 4%. Regulators used to recommend a 25% capacity surplus.

Sam Laidlaw, Centrica's chief executive, told the BBC: "No new power stations are being sanctioned at the moment because everybody is worried about the political situation."

In an eye-catching pledge at the Labour conference last year, Ed Miliband pledged to freeze energy prices for 20 months if he wins the 2015 election, while energy secretary Ed Davey has suggested that Centrica should be broken up.

Nick Luff, finance director at Centrica, said consumers would be forced to "shift their demand" for energy in the future by only using washing machines at night, for example if the situation were not resolved. He said factories may also be forced not to operate at peak times.

"The risk is on a cold still day in January when the wind turbines are not turning and demand is very high because it is cold," Luff said.

Caroline Flint, the shadow energy secretary, said: "It is not acceptable for companies to threaten that the lights will go out because they don't want greater transparency, competition and accountability. When markets aren't working government has a responsibility to step in. Labour's plans to reset the energy market will follow the price freeze in 2017 and help restore public confidence

"The reality is that what investors care about is long term certainty. ."

Laidlaw said Labour's pledge was not credible. "We firmly believe that any form of price control in a competitive market is not the answer and is not in the best interests of customers, and this has been clearly demonstrated by experience in other markets. Such proposals create both short-term uncertainty for all energy suppliers and longer-term additional costs for customers."

The blackout warning came as British Gas admitted it had lost 462,000 customers since January 2012, including 100,000 in the past seven weeks. The exodus of customers, higher costs and warmer winter weather dragged British Gas's annual profits down 6% to £571m.

The company still made an average profit of £37.60 from its 15.2m customers.

British Gas increased its tariffs by an average of 9.2% in November as part of a round of winter bill rises across the "big six" energy companies. It said the number of customers leaving was "stabilising" after it scaled back its price rise by 3.2%.

A spokesperson for the Department of Energy and Climate Change said: "We are acting to increase competition in the market and are working with Ofgem to make the retail market simpler and clearer for customers.

"Since 2010 the number of small energy suppliers has doubled, providing consumers with a real choice which has resulted in more than 1.5 million people switching in the last quarter alone, many to smaller companies."

Laidlaw said British Gas had "always been one of the first companies to reduce prices when the opportunity arises", but could not make any promises over prices for the year ahead.

Centrica's shares have lost more than a fifth of their value since Miliband's speech in September, with the stock driven down further after Davey called for a full-scale investigation into the energy market that could see British Gas broken up. Laidlaw said the company would find it harder to make big investments and secure big gas deals if it was forced to break up. "If we were broken up into smaller companies, we wouldn't be able to undertake the scale of activity," he said.

Laidlaw, who was paid more than £5m last year, admitted his pay was high but said executives needed to be paid well, especially if they had to cope with political attacks.

"I do believe that people who do a good job ought to be appropriately rewarded, particularly a very important job for the country in terms of bringing gas to Britain, in terms of investing in new sources of gas supply, investing in new power stations," he told Radio 4's Today programme. "These are jobs that are important for society and deserve to be rewarded.

"Like any business, you have to attract the necessary talent and this is a competitive marketplace and clearly, obviously, a lot of the politics doesn't make this more attractive as a place to work, so we need to obviously reward people appropriately."

Laidlaw pledged to give his bonus, which was worth £1.5m last year, to charity this year.