Table I. Vote share and seats won at the 2017 and 2015 UK General Elections in Great Britain.

Results from the constituency contested by the Speaker of the House have been excluded. Data from the British Election Study Constituency Results file vl .0.

Opinion polling is a major feature of British parliamentary election campaigns. Despite some clear failures—to identify the winning party correctly let alone each party's percentage of the votes (see Sturgis et al, 2016, 2017)—it is widely used by the print and broadcast media, often as their main stories, to chart a campaign's progress as well as to assess the relative popularity of government and opposition throughout a parliament's existence (on the polls generally, see the various chapters in Wring, Mortimore, & Atkinson, 2017). Most of the reported polls relate to the national situation, but a major innovation during the 2017 general election campaign is a harbinger of a probable future development that could have a major impact in a number of ways.