Sir Keir Starmer has said Labour under Andy Burnham would “harm” working people, comparing the Greater Manchester mayor to Liz Truss.
The prime minister warned there was “nothing progressive about abandoning fiscal rules” as he slammed Mr Burnham’s policies in a defiant interview with ITV Granada on Thursday.
It comes after growing speculation that the Greater Manchester mayor could mount a leadership challenge to Sir Keir after he told The Telegraph that Labour MPs are urging him to take the prime minister on amid tanking polls.
In a separate interview with the New Statesman, Mr Burnham said “we’ve got to get beyond this thing of being in hock to the bond markets” and called for key industries to be nationalised.
But speaking to ITV Granada, Sir Keir claimed Mr Burnham’s suggestions would “inflict harm” on working people, in a similar fashion to former Conservative premier Liz Truss’s disastrous tax cuts.

He said he would not “get drawn into commenting on the mayor’s personal ambitions”, but added: “I do want to be really clear about our fiscal rules, because economic stability is the foundation stone of this government.
“It was three years ago this week that Liz Truss showed what happens if you abandon fiscal rules. In her case, she did that for tax cuts, but the same would happen if it was spending.
“And we saw what happened to working people three years ago, the infliction of harm on them.”
The prime minister added: “I’m not prepared to let a Labour government ever inflict that harm on working people, which is why I’ve always been clear our fiscal rules are iron-clad, and that is because they protect working people.
“There’s nothing progressive about borrowing more than we need to. There’s nothing progressive about abandoning fiscal rules. They’re the foundation stone of this government.”

Sir Keir also insisted he would stay at the helm for the next general election. Speaking across a host of regional broadcast interviews, he said he wanted to “lead from the front” to take on “cowardly” Reform UK.
He added “we can and we will” change the country, in an apparent slap-down of Mr Burnham, and branded the Conservative Party “basically dead”.
He added his political project was a “10-year” endeavour and defended the government’s record a year into office.
Asked whether he could guarantee he would lead the ruling party into the next general election, Sir Keir said: “Yes. I’ve been very clear that this is a project of national renewal – patriotic national renewal – I was clear about that when we launched the campaign, as we did last year.
“I’m very clear that that is a 10-year project. I led from the front into the last election, I’ll lead from the front into the next election.”

He also criticised Mr Farage’s party, branding them “cowards” after the Reform UK leader of Nottinghamshire County Council appeared to ban councillors from speaking to journalists at a local newspaper.
There was a choice between “patriotic national renewal” under the Labour government, and “the politics of grievance, of toxic divide, which is what Reform are all about,” he added.
“It’s about the vast majority of reasonable, tolerant, decent people who want their country to be rebuilt and renewed, which is what we are,” he told ITV Calendar.
When asked whether he meant Reform voters were not decent, Sir Keir clarified: “No, of course they are, and they want the very best for their country. But Nigel Farage is interested in the politics of grievance.”