Andy Burnham’s July 2026 succession to Keir Starmer—following internal Labour rebellion, poor polls, and scandals—marks the latest in a string of short-lived premierships. Traders now assign an 85.5% chance that exactly two prime ministers will have served by the end of 2027 because Burnham enters office with a solid parliamentary majority, a mandate to restore stability, and no general election required until 2029 at the earliest. Labour’s unified leadership contest and Burnham’s early emphasis on long-term economic renewal reduce the near-term risk of another internal challenge. A third prime minister by late 2027 would require either a sudden leadership coup inside Labour or an unexpected loss of the Commons majority, scenarios priced at just 14%. Four or more would demand even more dramatic volatility that current conditions make remote.