Millions of households face energy bills rocketing to the equivalent of £367 a month over the winter.
Experts warned last week an energy price gas set by regulator Ofgem was on track to leap by around £1,300 to over £3,200 a year in October.
It could jump even higher in January - to more than £3,300 a year - if wholesale prices remain high.
Martin Young, a utilities analyst at banking and wealth management group Investec, said if that happens then the average household’s monthly energy bill would soar to the equivalent of £367 over the winter.
That is not what most households would actually shell out, however, as suppliers smooth the impact for those who pay by direct debit over the course of the year.
It means people tend to pay less than they actually use over the winter, with the opposite in the summer.
Meanwhile the chief executive of Ofgem has said the market price of energy is higher than it was at the time of the last price cap estimate.
In May, the energy regulator predicted that the price cap would reach £2,800 when it is next changed in October.
Speaking to MPs sitting on the Public Accounts Committee on Monday, while Jonathan Brearley refused to say if the cap could reach a figure of over £3,200 - as suggested by experts - he said energy prices appear higher than when Ofgem made its estimate.
He said: "It's clear given the pricing dynamics we're seeing, given the ongoing impact of the Russian invasion of Ukraine, that there is positive pricing pressure there - as in prices are looking higher than they did when we made that estimate - but we don't give ongoing sort of commentary until we make our formal announcement."
Around 76% of gas used by the average household throughout the year is over the winter.
Mr Young called the £367 a month prospect - even if smoothed out - “a truly devastating level for many.
“We have spoken in the past about ‘heat or eat’.
“The situation is getting worse, not better”, he said, adding “it is clear that more needs to be done.”
Under pressure, former Chancellor Rishi Sunak announced a package of measures in May to help households.
It included £400 for most customers later this year, with more for low income and pensioner households.
Ofgem hiked its price cap - impacting 23million households - from April to help energy suppliers claw back soaring wholesale costs.
The Mirror told how a headteacher was shocked to find out his school's energy bill is set to soar by a staggering £95,000.
Niall Smith, 51, said the electricity at Southborough High School, Surbiton, in Greater London cost £55,000 this academic year.
The cap for those on standard and other “default” tariffs jumped from an average £1,277 to £1,977 a year.
During the winter of 2020 into 2021 the average for the cap was £1,042.
Investec is forecasting the average could spiral to £3,285 a year in October.
If Ofgem decides to review the cap every three months - rather than the current six months - it predicts the level could jump to £3,359 a year.
Wholesale energy costs have been driven higher by gas-rich Russia ’s war in Ukraine.
It came as the biggest single pipeline carrying Russian gas to Germany began annual maintenance yesterday (Mon),. Flows are expected to stop for 10 days, but governments, markets and companies are worried the shutdown might be extended.
While little of the UK’s gas comes directly from Russia, it is heavily impacted by the wider rise in wholesale gas and electricity prices.
Wholesale gas prices here jumped 17% to 234p a therm by lunchtime yesterday (Mon).
While volatile, they were less than 10p a therm in May 2020.
Wholesale prices for gas to be delivered this winter are currently at a record high for this time of the year.
