This collection is comprised of data resulting from five internet surveys, conducted between 2015 and 2018. (1) A survey of 1193 Conservative Party Members, 1180 Labour Party Members, 730 Liberal Democrat Party Members, 802 United Kingdom Independence Party Members, 845 Green party Members, 968 Scottish National Party Members, conducted between 12th - 26th May 2015. It includes 347 variables relating to the political attitudes and activities, and demographic attributes of the respondents. (2) A survey of 5219 members of six British political parties (Labour, Conservative, Liberal Democrat, Green, UKIP and SNP) run immediately after the general election of June 2017; contains 436 variables on political attitudes and social background. (3) A survey of the political attitudes and social background of 2026 members of the British Labour Party, run in May 2016. (4) A survey of 2249 members of the Labour and Conservative parties undertaken in December 2018 on their attitudes towards Brexit. (5) A survey of 6378 strong partisan identifiers of six main British political parties, undertaken in May-June 2015. 258 variables on political attitudes and social background. (6) A survey of the political attitudes and social profile of 1759 trade union members. 224 variables.Few, if any, fully-fledged democracies prosper without political parties. But parties are in trouble almost everywhere - both in terms of public perceptions, which are becoming more and more negative, and in terms of membership numbers, which (with the exception of some newer, more radical entrants into the market) dropped considerably from the 1950s. However, most of the main British parties experiences unexpected upturns in membership recruitment from during the period covered by this project. Unless we are willing to see parties become essentially elitist, hollowed-out institutions, this should give us cause for concern. In a healthy democracy, parties cannot simply be brands run by elites for their own and for our collective convenience. They need to be rooted in, rather than disconnected from, society. Their programmes need to reflect meaningful differences. Their leaders and their parliamentary candidates are best chosen by competitive election rather than appointment or inheritance. Party members can help ensure that all this occurs in practice as well as in theory. They can also, of course, make the difference between a party winning or losing an election since contests are decided not merely nationally, in the media, but locally, on the ground. In spite of this, we do not know as much as we might do about party members in the twenty-first century. The Conservatives have, it is true, been reasonably well served recently, not least by our own surveys carried out in 2009 and 2013. However, the last academic survey of Labour members prior to this project was carried out in 1997 and the last survey of Liberal Democrat members in 1999. UKIP members had never been surveyed. Just as importantly, there has never previously been a study of the members of several parties carried out concurrently, thereby enabling researchers to ask them exactly the same questions at exactly the same time. Nor has there been any systematic study of people who leave political parties after joining them. The Party Members Project (PMP) changes this. Shortly after the general election of May 2015, using samples gleaned from the massive panels collected by internet pollsters, and therefore minimizing the logistical and other problems posed by enlisting the parties themselves, PMP conducted simultaneous surveys of the members of the UK's six biggest parties, along with Labour's trade union affiliated members and those citizens who felt strongly attached to one party or another yet did not choose to join them. Then, in the summer of 2016, the project surveyed Labour members again, following the unprecedented surge in that party's membership over the course of the preceding 12 months. Following the general election of June 2017, the members of the major six parties were surveyed again about their activities in the election campaign (among other things); those who had left their parties were also identified and surveyed about reasons for doing so. In December 2018, members of the Labour and Conservative parties were surveyed specifically about the attitudes towards Brexit.

Respondents were invited to complete a survey by email, sent by the YouGov panel management software. Invites are sent based upon the quotas for surveys currently in the field, but invites are not linked to a specific survey. Data collection information fro each survey can be found in the ReadMe file in the corresponding folder.