**Six UK parliamentary by-elections have already taken place in 2026, with a seventh widely anticipated before year-end, aligning with the market's strong preference for exactly six total outcomes.** The confirmed contests include Gorton and Denton (February, Green gain after a Labour resignation), three on 18 June (Makerfield for Andy Burnham's Labour entry, Aberdeen South Conservative gain from the SNP, and Arbroath and Broughty Ferry SNP hold), and Clacton (13 August, Reform UK hold after Nigel Farage's resignation amid a standards investigation). These stemmed from health issues, leadership maneuvers, Scottish Parliament moves, and personal/political pressures. Trader consensus centers on a sixth by-election in Holborn and St Pancras following Keir Starmer's recent resignation as MP, which is expected to proceed under standard writ timelines (typically 21–27 working days). The low probabilities assigned to seven or more reflect limited evidence of additional imminent vacancies from resignations, deaths, or disqualifications in the remaining months of 2026, consistent with historical patterns absent major scandals or mass retirements. Uncertainty around exact polling dates for the Starmer seat and any late developments could still influence the final count.