Liz Truss has come under fire from Dominic Raab, who has criticised her plans for an emergency tax-cutting budget which risks becoming an “electoral suicide note” for the Conservatives.

The Deputy Prime Minister, who is a supporter of Rishi Sunak for the Tory leadership, said Ms Truss is proposing “limited” tax cuts via her plan to scrap the national insurance hike, arguing it would “do little” for the most vulnerable.

He described the policy proposal as “bad politics” in remarks that continue the blue-on-blue attacks which have become a dominant feature of the race to replace Boris Johnson as the next Prime Minister.

Mr Raab wrote in The Times: “As Conservative Party members decide which way to cast their vote over the coming weeks, I urge them to consider this point carefully.

Rhyl Journal: Dominic Raab is backing Rishi Sunak in the Tory leadership vote (PA)Dominic Raab is backing Rishi Sunak in the Tory leadership vote (PA)

“If we go to the country in September with an emergency budget that fails to measure up to the task in hand, voters will not forgive us as they see their living standards eroded and the financial security they cherish disappear before their eyes.

“Such a failure will read unmistakenly to the public like an electoral suicide note and, as sure as night follows day, see our great party cast into the impotent oblivion of opposition.

“It will open the door of No 10 to Sir Keir Starmer, backed by the Lib Dems and the SNP — putting Brexit and the Union at risk, and ending the opportunity to make the 2020s a decade of low taxes and high growth.”

Ms Truss’s campaign has been forced on the defensive in recent days after the Foreign Secretary suggested there would be no “handouts” if she won the leadership contest and that her priority was reducing the tax burden.

But her allies have insisted she is committed to helping families struggling with soaring bills and further direct support has not been ruled out.

Ms Truss’s plan to reverse the national insurance increase, which Mr Sunak brought in as chancellor to boost NHS and social care funding, has come under fire for not offering enough to help the most vulnerable.

Mr Sunak has also signalled his plan would be to extend support packages he introduced during his time in the Treasury in a bid to ease the cost of soaring energy bills.