Energy bills will hit £4,266 for a typical household by January next year, warns consultancy Cornwall Insight.
That's a rise of £650 for households in England, Scotland and Wales compared with its estimate just last week.
Cornwall cited regulator Ofgem's decision to change the price cap every three months instead of six and higher wholesale prices for the sharp jump.
But Ofgem said no forecast for next year could be "robust" at this stage and had "limited value".
The higher estimate means that instead of £164 a month now, the average household would see bills jump to £355 a month at the beginning of next year.
Cornwall's warning comes as the government rejected calls for further help on energy bills until a new prime minister is in place. The CBI business lobby group said ministers must "grip the emerging crisis" and it "made no sense to wait" for a new Conservative party leader.
Downing Street said it would be up to the new leader make a decision on further aid for households.
In its latest report, Cornwall has also increased its forecast for this autumn's typical domestic energy bills to £3,582, up from its previous prediction of £3,358.
An Ofgem spokesman said: "The wholesale market continues to move extremely quickly so no forecast for next year is at all robust at this stage and will therefore have very limited value, especially for consumers who must always be the main priority.
"We cannot stop others from making predictions but we would ask that extreme caution is applied to any predictions for the price cap in January or beyond."
The latest price cap - the maximum amount suppliers can charge customers for average energy usage in England, Scotland and Wales for October - is due to be announced at the end of this month.
Dr Craig Lowrey, principal consultant at Cornwall said its price cap forecasts had been steadily rising but the big jump in its forecasts comes as "a fresh shock".
"The cost-of-living crisis was already top of the news agenda as more and more people face fuel poverty, this will only compound the concerns."
Earlier this month, the government announced how households in England, Scotland and Wales will receive that £400 to help with rising fuel bills this autumn with the money paid in six instalments.
But Dr Lowrey called on the government to use the latest predictions of higher bills to prompt a review of the support package being offered to consumers.
"If the £400 was not enough to make a dent in the impact of our previous forecast, it most certainly is not enough now. The government must make introducing more support over the first two quarters of 2023 a number one priority."
Sylvia Simpson, chief executive at Money Buddies in Leeds, told the BBC it had seen a 400% increase in people seeking advice from the debt help charity due to the rising cost of living.
But she said there was limited options for helping people with soaring energy bills: "The tools that we used to have before for example for switching utility providers to get the best deal - that has gone now. There is no switching to get the best deal anymore. People are really, really struggling."
She added: "We are dreading October. We know from the people that are coming to see us, they are not going to have enough money in October to deal with the increase in the fuel supply. The government needs to do something now."
Conservative leadership candidate Rishi Sunak has said he would provide more money to help people with their energy bills, if he becomes prime minister.
"As soon as we know how much bills will go up by, I will act," he said. His rival for the leadership, Liz Truss has pledged tax cuts to help people hit by cost of living increases.
But Liberal Democrat Leader Ed Davey has suggested that the government should scrap the energy price cap rise in October, which he said would save the typical household £1,400 this year. Mr Davey said the plan could be funded through backdating the windfall tax on oil and gas companies' profits.
'Panicking'
Dr Lowry said that without the more frequent changes to the price cap more energy suppliers might be in danger of collapse though he questioned the future of the price cap.
"After all, if it is not controlling consumer prices, and is damaging suppliers' business models, we must wonder if it is fit for purpose - especially in these times of unprecedented energy market conditions," he said.
In May, Ofgem said the typical household should expect to see an £800 increase in October, to £2,800 a year.
However, it subsequently admitted that "prices are looking higher than they did when we made that estimate".
The energy price cap sets a limit on the amount that can be paid for each unit of energy.
It is based on the price energy suppliers pay producers for electricity and gas.
This has risen sharply, fuelled by the war in Ukraine which has threatened supplies from Russia.
Many families are already facing soaring costs, with UK inflation - the rate at which prices are rising - at the highest in 40 years.
Personal finance expert Martin Lewis told the BBC people would be "panicking" over their energy bills, and warned it would "be desperate" when bills rise this winter.
"It's going to throw many households into a terribly difficult financial situation," he added.
Mr Lewis said that more needed to be done now to help the poorest households.
The Don't Pay group, which is demanding bills be reduced to to an affordable level, says tens of thousands of people have pledged to cancel their direct debit payments from 1 October.
However, charities have said not paying energy bills has very serious consequences for consumers, including being threatened with disconnection and damage to their credit rating.
Householders who are struggling to meet their bill payments are advised to contact their suppliers to come up with a payment plan.
Source: BBC
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