This paper will seek to provide an analytically robust explanation of the British Labour Party’s continuing decline. The chapter contends that the party’s degeneration and decay has commonalities with structural forces afflicting social democratic parties across Europe. The six changes mirror the core themes of this volume: first, class dealignment and the long-term erosion of the working-class; second, the Labour party’s cultural and political disconnection from working-class voters; third, an inability to respond to structural changes in the economy and labour markets arising from technological change, digitalisation and global economic integration; fourth, weakening of the traditional welfare state following the demographic shift towards an ageing society; fifth, the debate about immigration and multiculturalism which forced questions of national identity onto the political agenda in western European countries, uncomfortable territory for Left parties; and, finally, the long-term impact of European integration, resulting in the UK’s referendum decision in 2016 to leave the European Union (EU). Before analysing each of these factors in turn, the chapter briefly dissects the nature of centre-left decline in the UK.