The Party (un)Faithful: Explaining Disloyal Party Members’ Voting Behaviour in Belgium and the United Kingdom

It is often postulated that party members vote for the party they belong to. Recent research, however, suggests that considerable segments of party membership bases behave disloyally by casting a vote for another party (Polk & Kölln, 2016). As such, even the assumed ‘loyal’ and ‘vote-multiplying’ party members (Scarrow, 1994) seem to not necessarily provide an antidote against the high levels of voter volatility from which parties across Europe are suffering (Drummond, 2006). Using data from broad-scale surveys among party members in Belgium and the UK, we will further map out the share of party members that cast a defecting vote in elections and, more importantly, we aim to further extend our knowledge on why they do so. We try to explain this phenomenon by taking into account (1) programmatic considerations, related both to dissatisfaction with one’s own party and to the ideological ‘attractiveness’ of competing parties, (2) appreciations of party leaders and (3) strategic (voting) considerations. Moreover, our comparative research design enables us to uncover conditional effects of the party system and electoral system. We more specifically expect that strategic considerations are more important for defecting voting behaviour in the UK due to its single-member plurality system, and that programmatic considerations are more important in Belgium, as its highly fragmented multi-party system(s), as opposed to the UK’s two-party system, decreases the ideological distances between parties, possibly lowering the threshold for party members to cast a defecting vote. As such, our paper looks at intra-party cohesion from a rather novel perspective. We measure party cohesion at the level of the ‘party on the ground’, assess to what extent disloyal voting behaviour is used as a temporary ‘exit option’ for party members dissatisfied with their party’s functioning, and examine the individual and institutional-level determinants of cohesion among party members.