Gas and electricity bills will rise by more than £900 this autumn, one of Britain's biggest energy suppliers has forecast.
Keith Anderson, chief executive of Scottish Power, said ten million poorer households needed bill discounts of £1,000: five times more than the government plans to offer in October, as he warned time is running out for emergency support.
Households will be left with a "huge increase" in their bills and unable to top-up their meters unless ministers act now to establish an adequate support mechanism, Anderson said.
Energy bills surged by 54% last month to a record high of £1,971 a year for a typical home after rising prices forced Ofgem to increase the price cap on standard tariffs.
The cap is due to change again in October and high gas prices since Russia's invasion of Ukraine lead experts to believe that it will increase significantly.
His comments came as customers reported that their direct debits have doubled, despite the price cap being half that.
Scottish Power predicts that the cap will rise further than other recent estimates because of changes that Ofgem, the energy regulator, is considering to the way it is calculated.
We explain whether your supplier can increase your direct debit payments, here.
Anderson said: "Right now, on our forecast, we could see the cap in October going to £2,900."
The government arranged a £150 payment to four fifths of households via a council tax rebate last month and has said that every household would receive £200 off their energy bills in October, repayable in five annual instalments of £40 from next year.
But arguing that it is not enough. Anderson said energy costs will rise from just over £1,000 in January last year to almost £3,000 by October, leaving ten million households in fuel poverty.
"We think that's got to such a huge level that it requires a much, much more significant intervention than the proposals to date. My view is that we need an intervention of about £1,000," he said.
"If we leave the price at £2,900, debt levels are going to go through the roof because people will just be unable to pay."
He added: "The horrible truth is it means people will not be heating their home and they will not be using cookers and electricity because they can't afford to put money on the meter."
Scottish Power said any support needs to be signed off by July if it is to be implemented by October.
The company is suggesting payments of £1,000 to the ten million households most in need. It said the £10billion cost could be borrowed by the government then recouped through taxes or energy bills.
The government said: "We recognise the pressures people are facing with the cost of living, which is why we have set out a £22billion package of support, including rebates and energy bill reductions."
Ofgem is looking into claims that some suppliers increased direct debits by more than necessary after the price cap rise - however the three firms under investigation have not been named.
The Chancellor said the Treasury is working hard "to find ways in which we can continue to ease the burden for families".
The next Budget is in November is the earliest opportunity for state intervention.
Mr Sunak said: "We will look to do all we can to help people with energy bills in the autumn when we know more about what prices will be then.
"We have been in a position to step in and help financially, both at home and now in Ukraine, with billions of pounds of support because we have made responsible but difficult decisions to stabilise the public finances.
"By getting borrowing down and reducing our deficit, we have given ourselves room to put money aside for future crises.
"And that responsible management of taxpayers' money will only become more important in the coming months. As we saw with the Bank of England's updated outlook last week, things will continue to be challenging economically. I am working with my Cabinet colleagues to find ways in which we can ease the burden for families and we will look at all options."
