Andy Burnham, the mayor of Greater Manchester, is now a member of the U.K. Parliament after winning a special election in northwest England.

Burnham has said he intends to trigger a leadership challenge to unseat Prime Minister Keir Starmer and seize control of the Labour Party.

Two years after a landslide election victory, Starmer’s popularity has greatly diminished over a perceived lack of personality, and a series of policy U-turns and scandals.