Burnham has been elected as the leader of the governing Labour Party, securing the backing of 349 out of the party's 401 lawmakers. Given that the Labour Party holds a majority in Parliament, its leader automatically assumes the role of the country's Prime Minister. This transition occurred without the need for a general election.
Why Britain has a new Prime Minister without a general election
Burnham has become Britain's new Prime Minister after being elected leader of the Labour Party.
Source: The Business Standard