UK parliamentary by-elections occur when MPs resign, die, or otherwise vacate seats outside a general election, with writs issued under standard Commons procedures. As of early July 2026, four have been confirmed or held this year—Gorton and Denton in February, plus Aberdeen South and Makerfield in June—while a fifth in Clacton was triggered by Nigel Farage’s July 7 resignation amid standards scrutiny. Trader odds remain tightly clustered because the remainder of 2026 depends on unpredictable factors such as further Labour resignations tied to the ongoing leadership transition after Keir Starmer’s June departure, potential Scottish National Party or Reform UK vacancies, and routine health or personal exits. Historical base rates suggest several more could arise before December, yet the exact total hinges on whether political turbulence accelerates or stabilizes. Any additional high-profile departures before the autumn recess could quickly separate the 6–8 range.