Reacting to the announcement this morning, Mr Lewis said the most vulnerable will be hit hardest by soaring energy bills.
“I've been accused of catastrophising about the energy hikes that have now come true,” Mr Lewis wrote. “Yet let me be plain, 'doom-mongering' or not.
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“More help is desperately needed for poorest or people will die this winter due to unaffordability of an 80 per cent so far energy price cap hike,” Mr Lewis continued.
He added that the situation is a “genuine social and financial catastrophe that is putting lives at risk”.
“The price cap is actually a cap on the standing charges and unit rates that you pay, they have gone up by around 80 per cent.
“The figure that's quoted, the £3,549, is what the cap would be for someone who has typical usage - of course, most people don't have typical usage, they're more or less. That means there is no maximum amount that you can pay for gas or electricity.
“You could easily be paying £5,000 or £10,000 a year if you have high usage.
“I worry terribly for some of those who have disabled children or disabilities themselves who need lots of electrical equipment to keep their houses warm because of medical conditions.”
On the January price cap increase, Mr Lewis said costs could go up another 51 per cent.
“And that is not such a crystal ball prediction because we are seven months through the 10-month assessment period for the January price cap,” he said.
Mr Lewis added: “So if we look at the totality across the winter, from October until March, you are probably talking on typical use an average bill of over £4,400 a year, typical pro rata - it is totally unaffordable.”
It comes as chancellor Nadhim Zahawi said the increase in the energy price cap would cause “stress and anxiety” for people but that the government was working to develop more options to support households.
“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,” he said.
“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.”
Labour shadow chancellor Rachel Reeves said urged the government to act to protect the public from soaring energy bills. She accused ministers of being nowhere to be seen on the morning of the announcement.
The StepChange debt charity said a third of its new clients were in energy arrears in July, before the latest rise, and this could rise to more than half after the next price cap increase in January.
Chief executive Phil Andrew said: “Household budgets are being pushed to the absolute limit and it's inevitable this will lead to more people experiencing debt.
“The demand for debt advice is rising across the sector as the cost-of-living crisis bites.
“Many of our existing clients are also having to amend their arrangements as they can no longer afford their previous payments.”
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