Former Labour Prime Minister Gordon Brown has called for an emergency budget before the UK hits a "financial timebomb" this autumn.
Mr Brown said millions would be pushed "over the edge" if the UK Government does not address the cost-of-living crisis.
Conservative leadership rivals Liz Truss and Rishi Sunak have clashed over how they will address high inflation.
Mr Brown wants them to agree an emergency budget with PM Boris Johnson this week, or for Parliament to be recalled.
He said: "The reality is grim and undeniable - a financial timebomb will explode for families in October as a second round of energy price rises in six months sends shock waves through every household and pushes millions over the edge."
The BBC says a new report commissioned by Mr Brown, carried out by Professor Donald Hirsch from Loughborough University, found that 35million people in 13million households across the UK are under threat of fuel poverty in October.
This is "an unprecedented 49.6% of the population of the United Kingdom", said Mr Brown.
In Scotland, a person is deemed to be living in fuel poverty if, to heat their home to a satisfactory standard, they need to spend more than 10% of their household income on fuel.
In England, a household is said to be in fuel poverty if:
- They have required fuel costs that are above average (the national median level), and
- Were they to spend that amount they would be left with a residual income below the official poverty line.
Major blows to income
Findings from Mr Brown's report suggest the additional one-off £1,200 support for low-income households will fail to compensate for major blows to income from this October to October 2022.
Meanwhile, a senior ally of Liz Truss says she has not ruled out giving help to families struggling with the cost-of-living crisis.
Penny Mordaunt claimed that to say so was "overinterpreting" what Ms Truss had previously said.
The Foreign Secretary had said she would focus on "lowering the tax burden, not giving out handouts".
Mr Sunak has said she was "simply wrong" to rule out more cost-of-living payments.
Trade Minister Ms Mordaunt told the BBC that Ms Truss had not ruled out expanding direct payments to help people struggling financially.
In other political news, Ruth Davidson has declared that she would make a sensational return to front-line politics to lead the pro-Union campaign if there is a second independence referendum.
Ruth Davidson ready to serve
The former Scottish Tory leader said that, while she believed she would never again stand in a parliamentary election, she was ready to serve "in any way I can" should the SNP succeed in securing another vote on breaking up the UK.
The Telegraph says that, once touted as a potential prime minister, Ms Davidson transformed the fortunes of the Scottish Conservatives during her eight-year stint as leader, before standing down in 2019.
She denounced Nicola Sturgeon's latest plan for securing a new vote as a "sign of weakness" on the part of the SNP.