Brexit caused a structural shift in the electorate

The Labour Party’s strength stemmed from the alignment of the working-class with university-educated middle-class voters. Both groups came under the Labour banner because their economic interests aligned. They both wanted higher wages, stronger trade unions, quality and accessible public education and a world-class health system that was free at the point of use. ^[1] However, Brexit created a seismic jolt in British politics. The jolt pushed the economic interests of these two key demographics out of alignment. Unless it radically changed the core focus of the party, Labour was always doomed to lose the 2019 election. In the run-up to the 2016 referendum, there were already warning signs. The economic interests of the working-class had moved to immigration, while the middle-class had maintained their focus on wages, free trade and the free movement of people. The 2019 election was the result of these two core groups of Labour supporters falling out of alignment. Working-class voters flocked to the Conservatives over concerns that their economic interests were not being heard in Jeremy Corbyn’s Labour Party.

[P1] Labour relies on the support of the working-class and university-educated middle-class. [P2] The two demographics have traditionally shared economic interests. [P2] Brexit pushed the two group's economic interests out of alignment. [P3] This dismantled Labour's base and caused their election defeat.