Andy Burnham’s swift replacement of Keir Starmer as prime minister in July 2026, following Starmer’s resignation amid historically low approval ratings near net -60, has established two recent holders of the office. Traders assign an 85.5% probability to exactly two prime ministers by the end of 2027 because Burnham, a former Manchester mayor with stronger internal party support, faces no immediate leadership challenge and benefits from Labour’s large parliamentary majority. The slim 14.5% chance of three reflects risks from persistent economic pressures, Reform UK’s polling strength, and any early erosion of Burnham’s standing before the 2029 election deadline. A fourth or more remains remote at 1.5% given the absence of scheduled general elections or acute instability that could trigger another rapid turnover in the next 17 months.