Andy Burnham has pledged to provide immediate cost-of-living relief for Brits and "do politics differently" in his first speech after becoming prime minister on Monday.
Speaking outside his new official residence at 10 Downing Street shortly before 1pm local time (10pm AEST), Mr Burnham also gave his clearest signal yet he does not plan to alter the AUKUS defence partnership, in which Australia has already invested billions of dollars.
Mr Burnham officially rose to the United Kingdom's top political office on Monday, after a weeks-long process to replace the unpopular incumbent Sir Keir Starmer as Labour Party leader.
The new PM spoke without a lectern, something that represents a significant break with British tradition, and was surrounded by supporters on Downing Street.
Mr Burnham acknowledged the fact he was the country's seventh prime minister in 10 years.
"We will make this moment a circuit breaker for Britain," he said.
Andy Burnham makes a point to reporters on Downing Street. (Reuters: Temilade Adelaja)
Foreign leaders, including Australia's Anthony Albanese, were quick to congratulate Mr Burnham, a former long-time MP who had until last month served as the Mayor of Greater Manchester.
Now, he is in charge of the world's fifth largest economy.
"I look forward to working with you to strengthen our partnership and promote security, resilience and prosperity in the years ahead," Mr Albanese posted on social media.
While Mr Burnham has said little about foreign policies in the past few weeks, he did say on Monday Britain would honour its "defence commitments to international partners" in the clearest sign yet he does not plan to try and tinker with the AUKUS pact.
Signed in September 2021, AUKUS is set to cost Australia at least $300 billion over the next three decades. But the UK has had five PMs in that time, and concerns have been raised that Britain is struggling to keep up with its end of the bargain.
Andy Burnham and King Charles pose for a photo in Buckingham Palace's Chinese Dining Room on Monday. (Reuters: Aaron Chown/Pool )
Unlike in Australia, British prime ministers are not sworn in. Instead, they meet the monarch to take part in an ancient ritual called "kissing hands" (once there was an actual kiss, but these days it is just a conversation).
Mr Burnham arrived at Buckingham Palace about 12:05pm. His meeting with King Charles III took place in the Chinese Dining Room, a few minutes after Sir Keir had been there to tender his resignation.
After his meeting, Mr Burnham travelled to Downing Street where he made his address.
"Later this year, I will bring forward a new plan for Britain, a 10-year plan laying believe we all want Britain to be, wherever we're coming from, whatever party we support," Mr Burnham said.
"But I can do something to give people some breathing space now, some help with the cost of living. And I will set out some of those measures starting tomorrow, including how we pay for them."
Mr Burnham, a former minister in the Brown and Blair governments, has twice stood unsuccessfully to be Labour leader in the past.
Amid Sir Keir's plummeting approval ratings, Mr Burnham returned to national politics via a by-election last month.
As part of his platform, he plans to decentralise power from London and put key services under state control. He said on Monday he would "put people at the heart of everything I do".
"Let us make this the moment when Britain starts to believe again. The moment we bring back hope," he said.
Sir Keir Starmer and his wife Victoria were all smiles outside downing street. (Reuters: Kevin Coombs)
Earlier, Sir Keir gave his final address outside Number 10 Downing Street, the prime minister's official residence, where he said, "My work here is done."
"I go with good grace, I go with a smile, and I go proud of everything we have achieved," he said.
Of Mr Burnham, he said: "I wish him every success; he has my full support."
Sir Keir had been Labour leader for more than six years and had won a landslide general election victory two years ago.
However, he had become so unpopular in the UK, his position was seen as untenable by many Labour colleagues and when Mr Burnham returned to Westminster as an MP, he resigned a few days later.
Mr Burnham has not yet announced his first cabinet.
