The Foreign Secretary intends to hold an emergency budget in September if elected Prime Minister and would seek to axe the National Insurance rise within days rather than waiting until April in line with the usual Treasury rules.

The rise was introduced in April by her leadership rival Rishi Sunak in a measure intended to raise more money for the NHS and social care.

Ms Truss wrote in the Sunday Telegraph: “I would hit the ground running by bringing in an emergency budget, charting a firm course to get our economy growing in order to help fund our public services and NHS.

Liz Truss is on course to become the next Prime Minister

“I would use this to immediately tackle the cost-of-living crisis by cutting taxes, reversing the rise on national insurance and suspending the green levy on energy bills.”

The Foreign Secretary earlier insisted tax cuts, not “handouts”, would help families with rocketing fuel bills this winter.

Mr Sunak said: “It’s simply wrong to rule out further direct support at this time as Liz Truss has done, and what’s more, her tax proposals are not going to help very significantly people like pensioners or those on low incomes who are exactly the kind of families that are going to need help.”

It comes as Labour analysis found energy bills for pensioners are expected to be almost triple this winter what they were in 2020 - going up on average from £23 a week to £72. Even with October’s £400 rebate taken into account, they are expected to spend 18 per cent of their weekly expenditure on energy bills, up from seven per cent.

Jonathan Ashworth MP, Labour’s Shadow Work and Pensions Secretary, said: “Pensioners up and down country are worrying about how they’ll heat their homes this winter while Tory leadership candidates propose fantasy tax cuts that won’t get help to those who need it.”

A senior ally of Ms Truss said she was not ruling out providing further direct support to households over winter.

Trade minister Penny Mordaunt told BBC Radio 5 Live that the Foreign Secretary claimed that to say so was “overinterpreting” what Ms Truss had previously said.

Ms Truss had said she would focus on “lowering the tax burden, not giving out handouts”.

Ms Mordaunt said: “There’ll be different things required for different people - there’s the package of support that’s already been put in place [and] Liz is looking at other measures.”

Former Tory party co-chairman and Sunak supporter Oliver Dowden labelling Ms Truss’s proposed tax cuts “insufficient”.

He told BBC News: “You’re going to see energy bills going up to almost £4,000 and if you look at the idea of the tax cuts, this idea of reversing the national insurance contributions, that’s only going to benefit someone working full time on the national living wage by less than £60.

“Contrast that with whoever the prime minister is, they’re going to get a benefit of about £1,800.

“So this isn’t the way to help people through this very difficult period.”

Former Prime Minister Gordon Brown pressed both candidates to agree an emergency budget with Mr Johnson this week or risk “condemning millions of vulnerable and blameless children and pensioners to a winter of dire poverty”.

“The reality is grim and undeniable: a financial timebomb will explode for families in October as a second round of fuel price rises in six months sends shock waves through every household and pushes millions over the edge,” the former prime minister wrote in Sunday’s Observer.

His report found existing Government support for low-income households has fallen short of offsetting the losses they face, with some families up to £1,600 worse off a year.

The additional £1,200 offered to the poorest in society this year will fail to compensate for three major blows to their income from October 2021 to October 2022, the analysis suggests.

More than half of the public think the Government could do more to help with rising costs but is choosing not to do so, according to a poll by opinion research agency Public First.

The survey of 2,011 people also found that 64% are finding it difficult or impossible to pay energy bills.

Tory MP Damian Hinds conceded the package of support Mr Sunak drew up as chancellor was not enough in these “extraordinarily difficult times”, and suggested more would come if he became prime minister.

He told Sky News: “Things have been getting worse even since that was put into place in terms of projections for energy bills… and he’s been clear that more may well be needed and and he is ready to do that as required.”

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Pensioners face spending almost £1 in every £5 on energy bill this winter, Liz Truss warned