Sir John Major, the former Conservative prime minister, has said there is a case for an excess profits tax on the big six energy companies. He said the money could be used to help the poor as they struggle with massive energy bills this winter.

He claimed many people this winter will face a choice between eating or staying warm.

His remarks at a press gallery lunch in Westminster will be a severe political shock to Downing Street, which has insisted there is nothing the government can do to combat rising energy prices except urge consumers to shop around for cheaper tariffs or foster greater competition in the market.

The former Tory leader described recent hikes in electricity and gas bills of approximately 10% as "unacceptable".

He argued that the coalition needed to show that it was supporting "people, not institutions".

The Labour leader, Ed Miliband, has dominated the political debate on energy prices since his party conference speech promising a 20-month price freeze if he is elected in 2015.

Major's proposal is different since it is a tax on excess profits. The energy companies insist that price rises are not designed to increase profits, but are in response to increases in wholesale gas prices.

It is likely to be highly awkward for David Cameron that a former Conservative prime minister believes it is necessary to suggest such a direct intervention in the market at a time when the prime minister has dismissed Miliband's proposals as Marxist or a con.

Major, who is normally loyal to Cameron, may just be flying a political kite for a faction inside Downing Street. George Osborne, the chancellor, has previously imposed emergency levies on the excess profits of the banks, so such a measure is not anathema to Conservative thinking.

But there are practical difficulties and many of the energy companies insist they need the profits to invest in new technology and meet government-imposed green obligations. There is also an intense dispute between Ofgem, the energy regulator, and the energy companies on the precise levels of their profits. Ofgem has just announced a review of energy company profitability, following criticism in the summer by the Commons energy and climate change select committee of the lack of transparency by the big six energy firms.

Bosses from the big six are due to give evidence to the energy committee next Tuesday in a hastily arranged session.

Sir Robert Smith, the Liberal Democrat acting chairman of the committee, said: "The committee has today decided to call in the energy bosses in the context of the latest wave of price increases."

Three of the big six have announced price rises in recent weeks: 8.2% by SSE, 10.4% for electricity and 8.4% for gas by British Gas, and 9.3% and 11.1% respectively by npower.

The committee said the session will explore a range of issues, including reasons and justification behind recent energy price rises, the difference of pricing policies between energy suppliers, and how the transparency of energy company profits can be improved.