Professor Tim Bale, Professor of Politics at Queen Mary explores party-switching politics – including how many people switch allegiances and why they do so. He writes: "It turns out, however, that switching parties at grassroots membership level is by no means uncommon, even giving rise in some quarters to accusations of “entryism". The massive increase in Labour’s membership which accompanied Jeremy Corbyn’s elevation to the leadership in 2015 was often anecdotally associated, at least in the minds of his enemies (internal as well as external), with an influx of people who had previously belonged to parties on the far left fringe of the country’s politics."
This was covered in the Conversation