Intertwined fates? Members switching between niche and mainstream parties

Little attention has been paid to the process of members leaving parties in order to support other parties. Party developments in the UK in the 2010s provide an opportunity to analyse the determinants of members giving up their current party and joining a rival. We examine this issue using an original panel survey of 2,679 members of the Green Party of England and Wales. Our results show that members who joined the Greens motivated by concern about social justice are more likely to leave and support Labour after Jeremy Corbyn’s election as party leader. Members who joined to protect the environment are less likely to leave. Niche parties can attract members predominantly motivated by issues traditionally represented by a mainstream party but these members are more likely to leave the party again following a position change by the mainstream party.