The Clacton by-election on 13 August features an electorate of roughly 78,700 and a record 34 candidates on the longest ballot paper in UK parliamentary history. Traders assign the highest probability to the 20k-30k turnout band because the contest occurs during peak summer holidays, a period that typically suppresses participation in by-elections. Recent constituency polling and commentary have repeatedly described expectations of “very low” turnout, consistent with historical patterns where summer by-elections and high candidate counts reduce voter engagement. The 30k-40k range sits second as a modest upward adjustment if core Reform supporters mobilise despite the timing, while sub-20k and higher bands remain marginal given the absence of major campaign events or turnout-boosting factors in the final days.