We examine voting behavior and alliances in the House of Lords, the United Kingdom’s upper chamber, over a span of two decades. This period witnessed multiple changes in government composition and the pivotal 2016 Brexit referendum that reshaped British politics, allowing us to evaluate an upper chamber’s responsiveness to transforming political environments. By analyzing original roll-call data from 2000 to 2022 and employing ideal point analysis, our study points to a shift from alternating voting alliances to enduring government versus opposition voting blocs. We furthermore find evidence of a noticeable increase in peers’ attendance and a rise in government defeats since the Conservatives regained an absolute majority in the Commons in 2015. Our findings carry implications for the responsiveness of upper chambers to broader societal changes.