The next Prime Minister must act urgently to address the "national emergency" of spiralling energy bills as millions of households face paying £3,549 a year from October.
Regulator Ofgem confirmed an eye-watering 80% hike in the energy price cap for Brits on default tariffs from this month - with forecasts suggesting the cap could rise above £5,000 next year.
Ofgem boss Jonathan Brearley said the increase would be "devastating" for families and called for urgent Government intervention.
The Tories have been accused of being missing in action after spending the summer embroiled in the bitter contest to elect a new party leader.
No Government minister was sent out to do traditional morning interviews with broadcasters when the price cap was announced this morning.
Frontrunner Liz Truss promised to take action "immediately" to help the hardest hit families but didn't set out further details.
It comes after she derided "handouts" and said she would prefer tax cuts to help struggling Brits.
In a statement, Chancellor Nadhim Zahawi insisted "help is coming" and said he was urgently drawing up plans for the next PM to "hit the ground running" in September.
But Labour said it was a "national emergency" and called for energy bills to be frozen.
Mr Brearley told BBC Radio 4's Today programme: "The truth is this is beyond the capacity of the regulator and the industry to address.
"So what we are saying today is, look we have 10 days now until we have a new administration, have a new prime minister and a new ministerial team.
"What I am clear about is the prime minister with his or her ministerial team will need to act urgently and decisively to address this."
He added: "All of us with the Government need to get ahead of this problem and manage it on behalf of customers because, as you say, the outlook for winter without any action looks very difficult indeed."
Money Saving Expert Martin Lewis said it was a "catastrophe" and warned "lives will be lost" without urgent action.
“What is staggering is we have allowed this announcement to be made," he said.
"Why have we got to this announcement stage and still no help has been announced... It’s catastrophic.”
Shadow Chancellor Rachel Reeves warned the situation was a "national emergency".
She tweeted: "This is incredibly worrying and will strike fear in the heart of many families.
"We cannot wait any longer to act. This is a national emergency.
"The Tories must freeze energy bills now so households don’t pay a penny more in winter."
Charities immediately called on the Government to urgently extend the household support package announced in May - when the price cap was predicted to reach around £2,800 in October - "to prevent the bleakest of winters".
Adam Scorer, chief executive of fuel poverty charity National Energy Action, said: "Households need money in their pockets to weather this storm or we are going to see millions in dangerously cold homes, suffering in misery with unimaginable debt and ill health.
"Action is needed now to prevent the bleakest of winters."
Simon Francis, co-ordinator of the End Fuel Poverty Coalition, said the announcement was "like a dagger to the heart of millions of people up and down the country".
"As a result of the decision, parents will be unable to feed their children, the sick and elderly will be condemned to worsening health, disabled people will go without vital medical equipment and households will be forced into poverty for the first time in generations," he said.
"All the solutions lie at the Westminster Government's door, yet it is silent in the face of this looming disaster."
Chancellor Nadhim Zahawi said: “I know the energy price cap announcement this morning will cause stress and anxiety for many people, but help is coming with £400 off energy bills for all, the second instalment of a £650 payment for vulnerable households, and £300 for all pensioners.
“While Putin is driving up energy prices in revenge for our support of Ukraine ’s brave struggle for freedom, I am working flat out to develop options for further support.
"This will mean the incoming Prime Minister can hit the ground running and deliver support to those who need it most, as soon as possible.”
A Truss campaign spokesperson said: "Today’s announcement will cause grave concern to many people across the UK who will be worried about paying their bills.
“As Prime Minister, Liz would ensure people get the support needed to get through these tough times.
“She will immediately take action to put more money back in people’s pockets by cutting taxes and suspending green energy tariffs.
“This is on top of ongoing work such as the Energy Bills Support Scheme, which will see a £400 discount paid to consumers from October, and the £1,200 package of support for the most vulnerable.
“Liz will work flat out to deliver long term energy affordability and security, unleashing more energy by maximising our North Sea oil and gas production - helping keep bills down in the future.”
