**Six UK parliamentary by-elections have already taken place or been triggered in 2026, positioning it as the clear market leader at 73.5%.** These include contests in Gorton and Denton (February), Makerfield, Aberdeen South and Arbroath and Broughty Ferry (all June), and Clacton (August), driven by resignations linked to health issues, party manoeuvres, Scottish Parliament moves, and standards investigations. A sixth by-election in Holborn and St Pancras was triggered by Keir Starmer’s September 1 resignation, with the writ expected shortly. Trader consensus at 73.5% for exactly six reflects the recent pace of vacancies alongside the low historical frequency of additional by-elections in the final months of a parliament, while the 21.5% on seven accounts for the possibility of one further unexpected vacancy before year-end. No other confirmed triggers have emerged in recent weeks.