**The announcement of Keir Starmer’s resignation as MP on 1 September 2026 has triggered a by-election in the historically safe Labour seat of Holborn and St Pancras, with Labour due to select its candidate by 9 September.** Recent Camden local election results showed Labour ahead of the Greens (38.8% to 28.8% in relevant wards), yet the latter’s stronger 2024 performance in the constituency (10.4%) and protest voting patterns on issues such as Gaza policy have positioned Green leader Zack Polanski as a credible challenger if he stands. Multiple other candidates—including independents, Reform UK, Conservatives, and Liberal Democrats—are expected or confirmed to contest, which fragments the vote and sustains uncertainty while nominations remain open and no polling date has been set. Trader prices reflect this early-stage fluidity, with probabilities distributed across potential Labour nominees and leading challengers because the outcome hinges on the identity of Labour’s selected candidate, Polanski’s final decision, and any subsequent campaign dynamics or national polling shifts under Prime Minister Andy Burnham.