This article seeks to uncover the factors that led Prime Minister Theresa May and the Conservative Party to lose a huge electoral margin over the Labour Party in the 2017 General Elections. Their undecisive victory produced a minority government and made the Brexit negotiations with the EU more difficult. In the first part of this article I analyse the electoral campaign of the two major parties and the salience of different issues (including, obviously, Brexit) for British public opinion. In the second part, the analytical focus moves to the Conservative and Labour voters, and the impact of electoral turnout. In the third part, I explore the «Brexit effect» on the electoral results of the Conservative and the Labour parties, observing electoral change at the level of individual constituencies. Finally, the last section speculates on the implications of the results, particularly for party and party system change.