He is UK's sixth PM in last 10 years; vows cost-of-living measures in his first speech.

The United Kingdom's new Prime Minister Andy Burnham delivers a speech outside 10 Downing Street in London after taking office on Monday. [Isabel Infantes / REUTERS]

Andy Burnham is Britain's new prime minister. After meeting King Charles III at Buckingham Palace, Burnham officially took over from Keir Starmer, who stepped down after just two…