Andy Burnham’s July 2026 ascension after Keir Starmer’s resignation amid collapsing polls and party rebellions has established the current baseline of two prime ministers through the end of 2027. Labour’s commanding Commons majority and the fixed parliamentary term running to 2029 reduce the near-term risk of a snap election or fresh leadership contest, supporting the market’s strong consensus on exactly two holders of the office. Burnham’s early net favorability remains modestly positive despite softening approval and persistent voter concerns over the economy, immigration, and living costs. With no major by-election shocks or internal revolts reported since the transition, traders assign only modest probability to a third prime minister emerging before the deadline.