Britain's political future will be determined by which parties can turn the crisis of the established party system into an opportunity for realignment, just as they did 100 years ago.

The start of the long election campaign has a wearily familiar feel to it, as the two main parties slug it out over tax and spending plans. This is the stuff of elections, of course, and can be expected to dominate the months ahead. But its very familiarity also jars: we now have a truly multiparty system, not a two-party one, and there is a plurality of perspectives in British politics, not a duopoly. The election is likely to produce a hung parliament, and probably a minority government rather than a coalition. So the shape of British politics will not be determined by the spending plans of one of the two main parties, even if the choice between them is ideologically significant. The key question is whether the fracturing of the party system leads to a realignment of British politics, or just a messy inter-regnum while we await fresh elections.

Discounting the final months of John Major's administration, our last experience of minority government was in 1974, when Labour scraped its way back into government, called fresh elections within the year, and then turned to the Liberals to sustain it in office after 1976. After an initial burst of activity in Harold Wilson's final two years, it survived vote-to-vote until 1979, when Margaret Thatcher was elected and set about dismantling the institutions of the post-war settlement. This provoked the first realignment of the party system since the inter-war period, with the creation of the Social Democratic party. It gave Liberals and centrists the opportunity to re-establish themselves as an electoral force, but the effect was only partial: the party system became tripartite, but the first-past-the-post electoral system continued to deliver one-party government. This masked an underlying decline in the Tory and Labour vote shares, and it is only in recent years, with the emergence of Ukip, the SNP and the Greens, that electoral pluralism has become more visible and potent.

Whether this contemporary fragmentation of British politics will lead to lasting change in the party system may now turn not on the axis of social class, but on that of territory and the future of the British state. Here the parallel with the early 20th century is more enlightening than that with the 1970s or 1980s. Between 1910 and 1915, the UK was governed by a minority Liberal government with the support of a progressive alliance of Irish nationalists and the nascent Labour party. It passed historic welfare and trade union reforms, thereby opening the way for the emergence of the organised working class as a central actor in British politics, from which Labour would later reap the benefits. The Liberal prime minister, Herbert Asquith, also gave the Redmonite Irish Parliamentary party what it wanted, in the shape of the (still-born) Irish Home Rule Act. Until the first world war, when Asquith's weaknesses as a national leader became more apparent, eventually prompting Lloyd George to ally with the Conservatives to remove him from office, this was perhaps the most successful period of peacetime minority government in modern British history.

Importantly, however, it was also a period of profound realignment in the party system, which came about for two main reasons. The first was a secular change, with the emergence of the Labour party as the chief standard-bearer of progressive politics, supplanting the Liberals during the 1920s and 1930s. This process started in the Edwardian era and reached its apogee in the Attlee landslide of 1945. It would only start to unravel in the 1970s and 1980s, as the industrial working class went into decline. The second was conjectural: the Easter rising in 1916 transformed Irish politics and enabled Sinn Fein to annihilate the Irish Parliamentary party as the leading force in Irish nationalism. The latter were wiped out in the 1918 general election, followed in short order by the eruption of Ireland's war of independence. Within the space of a few years, the shape of British politics was transformed. In Scotland, Irish immigrant working-class voters transferred their loyalties to Labour, as did the Welsh working class, while the Liberals lost a core bloc of Irish allies in the House of Commons. The 20th century two-party system began to take shape, based on a reconfiguration of social class and territorial interests, in which the Liberals were the principal losers (although they would be compensated by the enormous intellectual influence Keynes and Beveridge exerted on Labour in 1945).

If the Easter rising has an analog today, it is the 2014 Scottish referendum. The contrast between the two could not be more stark, of course: one was a desperate and doomed act of violent blood sacrifice, the other a mass demonstration of peaceful, participatory democracy. But in effect, they may not be so dissimilar. The Easter rising precipitated a huge shift in Irish political opinion, which wiped out the established nationalist party. The Scottish referendum looks to have shifted a large section of Labour's Scottish vote decisively towards the SNP. If recent polls prove anything like prescient, a major transformation of Scottish politics is underway, the ramifications of which will be huge.

Unlike the Sinn Fein leader, ??amon De Valera, Alex Salmond will take up his seat in Westminster if he is elected in May, alongside a legion of fellow MPs. In all likelihood, he will seek a deal with Labour, although the outside chance of a devo-max deal with the Conservatives in return for full-blooded 'English votes for English laws' should not be entirely discounted (and it should be remembered that the SNP minority administration in Holyrood was often sustained between 2007 and 2011 with Conservative support). He could also seek to leverage the European question to the SNP's advantage, offering support for a referendum on the basis that Scotland wins either way: if the UK votes to leave the EU, the SNP will call a fresh referendum on independence. (There is an intriguing historical parallel between Europe, Ukip and Ulster Unionism and Irish home rule in this regard: when asked about the Ulster Unionist leader Henry Carson's armed resistance to home rule, Katharine O'Shea, Charles Stewart Parnell's widow, said of her late husband: 'Carson's little army would have appealed strongly to him – only he would have tipped the Ulster rebellion into the home rule cauldron and directed the resulting explosion at England.' If he is wily enough, Salmond could do the same with Farage, directing his English Eurosceptic populism against the union.)

The lessons from all this should be obvious. Minority governments succeed when they build alliances with a wider set of social and civic forces, and open up the potential for a reconfiguration of politics, as both Asquith and Salmond achieved in their different ways. They fail when they remain focussed solely on parliamentary survival, staggering from vote to vote until eventually they pass the initiative to the opposing block of interests, as happened in 1929–31 and 1974–79. The wider the party support (and not just from their MPs) that can be drawn into supply and confidence arrangements for a minority government, therefore, the better. In a progressive alliance, then, this would probably mean Labour, the Greens, the SNP and Plaid Cymru, pitted against a Conservative–Ukip bloc, with the Liberal Democrats and the Ulster parties in the fulcrum position. The centre ground remains important in British politics for this reason alone, if nothing else.

Public legitimacy is vital, and in May 2015 that will hang on the intersection of England's two unions: the UK and the EU. A minority Labour government, lacking a majority in England and supported by the SNP, that turns its face against an EU referendum will struggle for legitimacy, as would a Conservative minority government lacking the support of Liberal Democrats and meaningful representation outside the Midlands and southern England. Each faces the challenge of configuring a new set of broad and durable political alliances that can gather and sustain public support. Structured by this complex interplay of interests, Britain's political future will be determined by which parties can turn the crisis of the established party system into an opportunity for realignment, just as they did 100 years ago.