Andy Burnham will promise to give people “more breathing room” when he gives his first speech as prime minister outside No 10 on Monday.
He is expected to say he is “acutely conscious” of the UK’s high turnover of prime ministers – and that politics needs to be more stable and responsible.
And he is expected to characterise the moment as one of “reflection and resolution”, arguing Britain must be honest about the challenges it faces.
Burnham will officially replace Sir Keir Starmer and become the UK’s 59th prime minister – and seventh in 10 years – on Monday, following a meeting with King Charles III.
In a letter published on Sunday evening, Conservative leader Kemi Badenoch wished Burnham “every success” as prime minister, but warned he was entering office without “any clear plan”.
“You have refused calls to come to Parliament for questions from MPs, and you have not submitted yourself to serious media scrutiny,” Badenoch wrote.
“This is not a promising start.”
It also included a promise of Conservative support to cut the benefits bill, and urged the incoming prime minister to rule out any new tax rises.
The letter followed earlier remarks from Badenoch that Burnham was a “people pleaser” at a time when the country needed someone who could “take tough decisions, who can face down Labour MPs”.
Burnham was officially declared Labour Party leader on Friday following a short contest in which he was the only candidate, having secured the backing of 379 MPs.
Some opposition parties have urged Burnham to call a general election in order to ensure he has a mandate for his premiership.
However, earlier Labour’s deputy leader Lucy Powell insisted Burnham would stick to the promises made in Labour’s manifesto in the 2024 general election but will be more ambitious.
“He really understands the bigger, bolder measures that are needed to live up to the manifesto promises,” she told the BBC’s Laura Kuenssberg programme.
In his maiden speech on Monday morning, Burnham will reportedly set out his domestic priorities.
The Makerfield MP and former mayor of Greater Manchester is expected to argue that political stability must deliver “tangible” improvements along with “giving people more breathing room” on the cost of living.
But it is not yet clear who Burnham will appoint in his top team. He is expected to start appointing his senior ministers once inside No 10.
There has been fevered speculation as to who will get which job, particularly the crucial position of chancellor.
Energy Secretary Ed Miliband had initially appeared the most likely candidate, but in recent days Home Secretary Shabana Mahmood has emerged as another potential replacement for Rachel Reeves at the Treasury.
The incoming prime minister’s team has already teased some of the measures Burnham is expected to take in his first months in charge.
This includes scrapping plans for a government-issued digital ID for all British adults, in what has been called a “reset of priorities” for Burnham.
Plans for new oil and gas drilling in the North Sea are also expected to be on the agenda, forming part of a flurry of measures from Burnham including plans to take water and energy companies under public control and a new council house-building programme.
But environmental campaigners have urged Burnham to stick to Labour’s 2024 manifesto, which promised not to issue new licences for North Sea drilling, arguing they would not reduce energy bills.
While details of the oil and gas plans are not yet clear, the incoming prime minister is expected to uphold the manifesto commitment, and only produce oil and gas at sites that already have licences.
On Sunday, US President Donald Trump welcomed the move for more drilling in a post on social media.
