This survey was conducted shortly after the UK general election of December 2019. The survey is the sequel to the Party Members in the UK 2015-2018 study. It covers samples of members of 6 British political parties and the Brexit Party, including 1179 Conservatives, 1357 Labour members, 1028 Liberal Democrats, 1158 Brexit Party supporters and UKIP members, 1023 Green Party, and 1026 SNP members. It includes 166 variables relating to demographics, political attitudes, voting behaviour, campaign activity, and the timing and duration of party membership. It is the first known survey to assess the movement of people between political party memberships in the UK.Members are a vital resource for political parties - particularly at election time. By surveying members of six political parties we explore just what they do for their parties during campaigns and whether that is changing over time, particularly as new forms (often online forms) of campaigning replace (or at least supplement) the old way of doing things. We also find out how members feel about something that has proved particularly controversial at this election owing to story-upon-story of parties having to suspend people from standing - namely the selection (and vetting) of candidates. And we look at the demographic characteristics and attitudes of party members: how much do they vary and change over time, and how representative (or unrepresentative) are members of their parties' voters? Finally, we investigate whether there has been much movement of members between parties, and in particular whether 'Remainers' have moved from the Tories and Labour to parties like the Lib Dems and whether Leavers who might previously have belonged to UKIP (and perhaps support the Brexit Party) have switched to membership of the Conservatives.

Respondents were invited to complete a survey by email, sent by the YouGov panel management software. Invitations are sent based upon the quotas for surveys currently in the field, but invites are not linked to a specific survey. It includes 6823 respondents who were either members of 6 political parties (Conservative, Labour, Liberal Democrat, Green, SNP and UKIP), or registered supporters of the Brexit Party at the time. The survey was conducted online by YouGov, and generated 166 variables. YouGov recruited the survey respondents from a panel of around 1 million volunteers who are given a small reward for completing a survey. Upon joining the YouGov panel volunteers complete a survey asking a broad range of demographic questions which are subsequently used to recruit respondents matching desired demographic quotas for surveys. Potential respondents for the party member survey were identified from questions asking respondents if they were members of any of a list of large membership organisations, including the political parties. At the beginning of the fieldwork period more than 9000 YouGov panellists who were party members were invited to take part in the poll, and 6823 respondents subsequently took part in the survey, effectively a response rate of over 70%. The data are not weighted in any way since there are no known official population parameters for the various party memberships. However, previous YouGov party membership surveys using unweighted data have generated predictions for party leadership contests that came very close to (that is within 1% of) the final official outcome, which gives us confidence in the quality of the data. For further details on YouGov methodology see: https://yougov.co.uk/about/panel-methodology/