Andy Burnham’s confirmation as Labour’s candidate in the Makerfield by-election, approved by the party’s National Executive Committee on 15 May following Josh Simons’s resignation, underpins his 58% implied probability. The seat’s long-standing Labour dominance, reinforced by Burnham’s personal popularity and local ties as Greater Manchester mayor, supports this positioning despite the constituency’s 2024 general election margin narrowing to 13 points. Robert Kenyon of Reform UK holds 36.5% on the back of the party’s strong performance in recent local contests across the area, where it captured significant council seats. Minor candidates trail with low single-digit odds reflecting limited organisational reach and historical vote shares below 5%. Traders weigh Burnham’s profile against Reform’s momentum ahead of the 18 June poll.