The cost of energy for British consumers will rise by 80 per cent from October, regulator Ofgem said on Friday, taking average annual household bills to 3,549 pounds ($4,188).
Ofgem Chief Executive Jonathan Brearley said the rise would have a "massive impact" on households across Britain, and another increase was likely in January, reflecting significant pricing pressure in energy markets.
He said the government needed to deliver further help to households.
"The government support package is delivering help right now, but it’s clear the new Prime Minister will need to act further to tackle the impact of the price rises that are coming in October and next year," he said.
"The response will need to match the scale of the crisis we have before us."
Finance minister Nadhim Zahawi said he was working on a plan to be ready for the next government, which will be appointed when either Liz Truss or Rishi Sunak becomes prime minister on Sept 5.
Ofgem said it was not giving projections for January when a new cap will take effect because the market remained too volatile, but it said the market for gas in winter means that prices could get "significantly worse" through 2023.
Energy bills have soared this year after wholesale gas and power prices, already rising after the pandemic, surged following Russia's invasion of Ukraine and Moscow's move to curtail gas exports to Europe.
The new average bill for electricity and gas for 24 million households means energy bills will have almost trebled from October last year when they were an average of 1,277 pounds, a major factor in inflation rising to a 40-year high.