"Britain needs to show the world that we can regain our stability," Burnham said in his first speech outside Number 10.
"I have just come from Buckingham Palace, where I have accepted His Majesty the King’s invitation to form a government," he said, opening in the traditional manner.
Breaking with convention, however, the new prime minister spoke not from a lectern but standing freely outside the famous door of 10 Downing Street.
Burnham acknowledged he is the seventh prime minister since 2016, and said the challenge for his government would be to restore stability and "to make politics work."
He pledged his administration would deliver "the biggest changes in the last forty years," both in politics and the economy.
Burnham promised a new 10-year plan for Britain later this year, but said he would act sooner to ease the cost of living, with details to follow "starting tomorrow."
He is the seventh Labour prime minister in British history, and the seventh UK prime minister since the 2016 Brexit referendum.
Burnham was born in Aintree, near Liverpool.
He served as MP for Leigh in the north of England from 2001 to 2017, holding posts including culture secretary and health secretary under Gordon Brown.
After Labour's 2010 election defeat, he held the health and education briefs in Ed Miliband's shadow cabinet.
From 2017 until June 2026 he was mayor of Greater Manchester, where he built his political base.
His predecessor, Keir Starmer, gave a farewell address outside Downing Street earlier, saying that after two years in office the UK was stronger and fairer.
Starmer became prime minister on 5 July 2024, the first left-wing leader since 2010.
He announced on 22 June that he would step down, amid poor poll ratings and discontent within his party.
Burnham was elected Labour's new leader on Friday – his third attempt at the job, having previously lost leadership contests to Ed Miliband in 2010 and Jeremy Corbyn in 2015.
Polish Prime Minister Donald Tusk congratulated the new British PM on social media, writing: "Poland and the United Kingdom are close friends and allies."
I look forward to working together with you for a stronger and safer Europe," Tusk said.
(jh/ał)
Source: PAP