Delayed shock? How Brexit conditioned campaign effects in British general elections

The impact of campaigns on electoral performance is conditioned in part by contextual effects. The popularity equilibrium model has proven to be an important guide to how the electoral effects of local campaigns vary by a party’s existing level of popularity. Such an equilibrium can, however be disturbed by an electoral shock—a rare event which fundamentally challenges the foundations that underpin predictability in elections. This article analyses the impact of the electoral shock of the UK’s 2016 referendum on EU membership on campaign effects in the subsequent elections of 2017 and 2019. Using a novel theoretical and methodological approach, it shows that while there were observable effects of the Leave vote already present before the referendum, the geography of the effectiveness of Labour and Conservative local campaigns was altered after the referendum. However, it was not until the 2019 election that the shock of the 2016 Leave vote became a particularly important predictor of the electoral efficacy of both parties’ campaigns.