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.
The warning comes as the government rejects calls for further help on bills until a new prime minister is in place.
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.
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 page 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."
However, he did say that without the more frequent changes to the price cap more energy suppliers might be in danger of collapse.
"Many may consider the changes made by Ofgem to the hedging formula, which have contributed to the predicted increase in bills, to be unwise at a time when so many people are already struggling.
"However, with many energy suppliers under financial pressure, and some currently making a loss, maintaining the current timeframe for suppliers to recover their hedging costs could risk a repeat of the sizable exodus seen in 2021."
He called on the government to use the latest predictions of higher bills to "spur on a review of the support page being offered to consumers".
However, he said rather than "critiquing the methodology of the cap", it may be time to consider the cap's place altogether.
"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."