Andy Burnham is meeting Labour MPs to "win their confidence" as their next prime minister, former Labour deputy leader Harriet Harman has revealed.
The former Manchester mayor is meeting groups of MPs from Monday, after being sworn in as Labour's newest MP, "to set out to them his programme, in order to win their confidence", Baroness Harman told Sky News' political editor Beth Rigby on the Electoral Dysfunction podcast.
Politics latest: Burnham sworn in as MP
Questions have surrounded Mr Burnham, who won the Makerfield by-election on Friday, about his policies as he looks set to replace Sir Keir Starmer uncontested.
If no other Labour MPs get enough nominations (81) to win a place on the ballot, he could become Labour leader, and therefore prime minister, as early as 17 July after nominations close the day before.
Baroness Harman, who was in Gordon Brown's cabinet with Mr Burnham, said: "He needs to demonstrate that in the interim period between now and 16 July, that he has won the confidence of the overwhelming majority of the Parliamentary Labour Party.
"And what he is doing from today is meeting groups of MPs, meeting them in order to set out to them his programme, in order to win their confidence.
"I think he'll need to set out his programme as well to the public, because he hasn't been able to set out his big picture for the future of Britain, what he thinks about Britain's role in the world, what he thinks about major economic issues.
"He will need to set all of those out now.
"So, we're in for an important period, but he's going to need to keep up the momentum. He's got amazing momentum from that by-election and he's going to need to keep up the pace."
Read more: How will a new PM be selected - and when will it happen?
She added that Mr Burnham is a "novelty now" but said he has "also got experience because he's been in the cabinet" and has the experience.
But, she added: "He's not tainted by this most recent cabinet's travails, so I'm very hopeful."
She said when he was culture, media and sports secretary, "he didn't make a huge impact on me until it came to the Hillsborough issue".
Mr Burnham was heckled and booed by a crowd of more than 24,000 people while delivering a speech at the 20th anniversary memorial service of the 1989 Hillsborough tragedy.
He said this prompted him to change his perspective and persuaded Mr Brown to release all official documents relating to the disaster, leading to the creation of the Hillsborough Independent Panel, which exposed the widespread police cover-up. He has continued to work closely with the bereaved families.
Baroness Harman added: "I saw a real determination that he really stood for something, that this was an unpopular issue to be constantly raising in the cabinet."
(c) Sky News 2026: Andy Burnham meeting Labour MPs to 'win their confidence' as next PM
Former DUP leader Sir Jeffrey Donaldson found guilty of historical rape and indecent assaults against children
Starmer quits: The economic statistic that will haunt his legacy
Man accused of drugging wife to rape her with others admits sex offences
Man charged with five counts of attempted murder linked to terrorism
Why did Sir Keir Starmer resign?
Six-year-old girl dies after collision with van in Newry, says Police Service of Northern Ireland
Toddler in stable condition after crocodile attack at Cambridgeshire zoo
Wowcher apologises over email that referenced crocodile attack on boy
Boy charged with murder of teenager who was stabbed to death in south London