To transform the political landscape, there needs to be a crucial issue about which both active politicians and grass-roots voters feel sufficiently betrayed in both their interests and their sentiments that they are angry enough not only to rock the boat but to sink it completely.  

The following attempt to apply historical lessons to present-day politics was published in the parliamentary magazine The House in April 2015 – which now seems a very long time ago.  Readers may judge whether it remains relevant.

Elections are usually decided by floating voters. Even important elections may turn on relatively small shifts: Labour’s 1945 landslide saw its share of the vote only 10 percent higher than in its 1930s doldrums, despite the upheavals of depression and war. Really momentous shifts – those that make or break generations of political predominance – depend not on floating voters or even on single elections, but on permanent changes among core supporters.

In many democracies, not only ours, the core remains faithful for generations, held together by solidarities, emotions, interests, family traditions, and regional loyalties. Big shifts in Britain have been few but historic. When the Whigs quarrelled over the French Revolution, they put Pitt and his successors into office for the best part of forty years. When the Tories split over Corn Law repeal in 1846, a new Liberal Party based on Free Trade and Nonconformity remained predominant until the 1880s. When the Liberals broke up over Irish Home Rule in 1886, the Conservatives became the major force in politics for a generation. The Liberals’ slow decline resulted in near extinction after a split during the First World War led to their replacement as the main anti-Tory party by Labour in 1922. Labour’s rise was then crippled when it too split over supporting a coalition government in 1931. These divisions permitted a long Conservative ascendency from Baldwin to now – nearly 65 years in office compared to Labour’s 38 – perhaps now petering out.

What do these major changes have in common?  Underlying them is a build-up of political tensions and socio-economic changes. The Tory row over the Corn Laws was foreshadowed by quarrels over Catholic emancipation, while the once unassailable landed interest was being overtaken by a rising urban population. The Liberal split over Home Rule followed a progressive radicalization of the party which marginalized its traditional element. Labour’s 1931 collapse stemmed from its inability to cope with the Depression.

To catalyse the underlying changes, there needs to be a crucial issue about which both active politicians and grass-roots voters feel sufficiently betrayed in both their interests and their sentiments that they are angry enough not only to rock the boat but to sink it completely. Such an issue was Sir Robert Peel’s scrapping of the Corn Laws, a threat to rural England and a reversal of electoral pledges: a leading back-bench rebel attacked him for ‘double-dealing with the farmers of England, betraying our constituents. What I cannot bear is being sold.’  Liberal unionists accused W.E. Gladstone of wilfully breaking up the United Kingdom and abandoning Irish Protestants. Labour activists tore down posters of Ramsay MacDonald as a traitor to the party.

Sometimes there comes an unpredictable accident – trivial or serious – that makes a difficult situation unmanageable. The arrival of an unknown potato blight from America in 1845 forced Peel to rush to end the Corn Laws. The 1885 general elections gave the Irish Nationalists the exact number of seats to hold the balance of power, thus pushing Gladstone’s fateful offer of Home Rule. George V unexpectedly asked MacDonald to form an emergency National Government because the Conservative leader Stanley Baldwin happened to be out of the country.

The consequence in all these cases was a long-term realignment of political forces, as traditional loyalties were renounced, local organizations broken up, and new alliances formed. Ingredients for such changes are visible today in what many see as a general crisis of democracy across the Western world. But will there be in addition some historic seismic shift?  Will Europe divide Conservative support? Will the Liberals be decimated – yet again? Will core Labour voters stream away to UKIP and Celtic nationalists? Will some unexpected turn of events – a scandal, a blunder, a disaster – disrupt the calculations? All these outcomes are easily imaginable. But only a referendum on Europe obviously combines the grass-roots toxicity of the Corn Law issue with the patriotic emotions aroused by the Irish Question, and therefore has the potential to remake the political landscape almost overnight.

When I wrote the above in 2015, I imagined a new landscape forming of a Left-wing constellation of a shrunken Labour Party, nationalists and Greens; a ‘New Progressive Party’ of ‘modernisers’, led, I imagined, by Cameron and Clegg; and a ‘British People’s Alliance’ of disgruntled Tory Brexiteers and UKIP.  But in the last general election, when Labour and Conservatives both claimed – it now seems duplicitously – that they accepted Brexit, they eclipsed the Lib Dems and UKIP. So Labour and Tory dominate again, but both are deeply divided. Consequently, the political and indeed cultural conflict that is convulsing the country is not being fought out between parties, but within them, making both extremely unstable. This makes the final outcome unpredictable. But it also makes some profound political realignment seem not less likely, but more.

Robert Tombs is professor of French history at St John’s College, Cambridge. His most recent work is The English and Their History (2014).