There is ample evidence that the 2016 Brexit referendum polarized British society and political elites, but the ramifications for voting alliances in the House of Lords, the UK’s upper chamber, are less well-known. We examine whether new voting alliances have emerged since the referendum and how lasting these alliances were. Analyzing original roll call data between 2000 and 2022, we find that government defeats have become frequent since the Conservative government took office in 2015, attendance in divisions increased, and a new alliance between Labour and Liberal Democrats remained strong even as the parliamentary agenda has been less dominated by Brexit legislation in more recent years. Our results speak to the ongoing debate over whether British politics has undergone a process of realignment and yield implications for the responsiveness of upper chambers to societal change more generally.