THE distance between the front benches in Britain’s House of Commons, it is said, is that of two drawn swords: it is a fittingly archaic and combative conceit. The Victorian chamber is not as urgently in need of rebuilding as some of the Palace of Westminster—it does not actually leak, falling bits of cornice do not routinely endanger life and limb, the electricity supply is reasonably reliable—but it is still arranged for the politics of a bygone era. Members of Parliament are arrayed behind the ministers and shadow ministers to whom they owe their tribal loyalty; at Prime Minister’s Questions jeers, roars and braying from both sides reverberate from the oak panelling. “I count my blessings for the fact I don’t have to go into that pit,” President George H.W. Bush once remarked.

The pit is the product not just of Parliament’s adversarial architecture, but of the electoral system that supports it. The MPs in the House of Commons, the elected and more powerful of Parliament’s two chambers, are the individuals who won the largest share of the vote in each of 650 constituencies. This constituency-winner-takes-all system, known rather oddly as “first past the post” (FPTP), took its current form in 1885. By its nature, FPTP squashes small political parties; the dynamics of what political scientists call “Duverger’s law” doom them to irrelevance or merger, a process that will reliably lead to duopolies on power. Defenders of FPTP argue that by giving voters two broad parties to choose between, instead of a plethora of more focused ones, it delivers durable single-party governments rather than flimsy coalitions. This allows governments to do more—and lets voters hold parties to account for either doing or not doing in office what they promise to do at elections.

The system’s detractors say that disenfranchising people who vote for small parties is a price that outweighs these purported benefits. And this problem has recently been getting worse. The general election to be held on May 7th will see some widely popular parties winning very few seats, but it is quite unlikely to produce a strong single-party government. If increasing costs in fairness offer fewer compensating benefits, both Britain’s people and its politicians may decide it is time for a change.

Not a tale of two parties

The most two-party election held since FPTP took its modern form was that of 1951 (see chart 1); the Conservatives got 48% of the vote and Labour got 49%. It was a time when class loyalty trumped almost all other concerns. A study of Labour supporters in Bristol in 1955 found that only a third held political views vaguely resembling the party’s; the rest presumably voted for it because their families, neighbours and workmates did. At the other end of the scale the Conservatives were the only game in town.

Now people do not feel so constrained. “My father was a steelworker, my uncles went down the mines,” explains Peter Short, who last year stood as a council candidate for the UK Independence Party in Yorkshire. “I was a Labour voter all my life. But I’ve had it with them.” Much the same can be heard from new supporters of the left-nationalist SNP and the left-somewhat-libertarian Greens. All told, UKIP, the SNP and the Greens commanded one in 18 votes in the 2010 election. Some polls put the equivalent figure today at around one in three. The share of the vote for the biggest two parties in May may be below 70% and could fall nearer to 60%.

Party activists are redesigning their canvassing sheets to accommodate newly nuanced voting intentions: “I suppose I am your classic Tory-Green-Labour swing voter,” says one resident of Cambridge, a seat so plural that five parties could all win more than 10% of the vote there. A number of previously safe seats are up for grabs, not because they will be lost to the new parties, but because those new parties will eat into past margins of victory. John Curtice, a psephologist, predicts a “lottery election” in which small shifts in the vote will make big differences in the Commons.

The complexity is in part a reaction to Britain’s first coalition government for 70 years, which has left its members with weakened flanks. The Conservatives have lost right-wing voters to UKIP. The Lib Dems have lost some more left-wing voters to the Greens and Labour. Labour, for its part, has seen its support in Scotland plummet after campaigning against independence in last September’s referendum. Stagnant living standards, blamed by each of the major parties on the other, have fuelled a “stuff the pair of them” attitude which benefits the small fry.

But longer-term trends are also in play. Half a century ago one in four voters said they identified with one of the main parties very strongly; now only one in ten does. Under Margaret Thatcher and Tony Blair this breakdown proved quite compatible with two-party politics. In the 1980s Thatcher courted working-class voters who would once have reflexively backed Labour; Mr Blair turned the tables a decade later. But either because the process has gone too far, or because they have no similarly gifted successors, neither of the two big parties now seems able to turn the collapse of allegiance to its advantage.

Who’s like us?

A second, related trend is that voters expect more from politics. They are more used to “shopping around” in their everyday lives, says Tim Bale, a political scientist at Queen Mary University of London. But whereas supermarkets offer wider choice and better value than ever before, politics does not. Quality has not improved and the differences between parties seem to many to be harder to see. Ever fewer politicians have significant experience outside Westminster. And FPTP means that many hardly even need to try and sell themselves. In 69% of seats the incumbent has a majority of ten percentage points or more; in those seats only half the voters had any contact with a politician in 2010. Voters paid no heed by the big parties return the favour.

The resultant disdain encourages people to vote for marginal candidates—what, after all, are they losing—or not to vote at all. In 1979’s general election 76% of voters participated; by 2005 turnout had fallen to 61%. The proportion rose slightly to 65% in the narrow 2010 election and may nudge up a little further this time. But the trend in safe seats is clear. A 2012 by-election in the utterly safe Labour seat of Manchester Central achieved the dubious honour of the lowest turnout in an election since 1945. Only 18% of voters participated.

The third and possibly most significant trend is a change in the shape of politics. A two-party system works best when debates can be collapsed onto a single axis—say from command-and-control economics to free markets. In Britain as elsewhere such a one-dimensional scheme does ever less justice to how people think. As class has lost salience, cultural issues have increasingly taken its place as a way of defining people’s politics. This has been helped along by the unusually large gulf in the experiences of younger voters and older ones that has come with the huge expansion of higher education over the past few decades. James Tilley, an Oxford academic, has argued for a while that Britain’s political maps are increasingly in need of a libertarian-authoritarian axis to supplement the old left-right economic axis. The rise of fresh-faced (if bearded) libertarian Greens and the support greying authoritarians offer UKIP proves he is on to something, though the fit is far from perfect: there are libertarian ‘kippers, including Douglas Carswell, one of UKIP’s two MPs; Green do-what-thou-wilt-ishness does not extend to fox hunting.

The politics of national identity have strengthened too. UKIP is a beneficiary; the SNP is another. Represented in Westminster since the 1960s, for decades the party defined what it was to be marginal. The devolution granted to Scotland in 1998—designed in part to sate the appetite for self-rule—provided it with a Scottish Parliament at Holyrood which included a degree of proportional representation (PR); its seats are allocated more or less in line with the popular vote. Re-energised and able to make every vote count the SNP became a minority government in 2007 and won an absolute majority in 2011, when it promised an independence referendum.

It lost the referendum, but its fortunes are better than ever. In Cumbernauld, Kilsyth and Kirkintilloch East, a seat east of Glasgow until recently as solidly Labour as Manchester Central, SNP membership has surged from some 300 before the referendum to over 1,600 now. Local members are dazzled by their success: one branch had to move its meetings from an official’s living room to a school gymnasium. “We are struggling to train people as fast as they join,” buzzes Jamie Hepburn, the local SNP member of the Scottish Parliament. Some polls have the SNP winning 40 of Scotland’s 59 Westminster seats in May.

The party is popular because it has successfully promulgated the idea that Scots are different: given to tolerance, solidarity and greenery in a way that sets them apart from the right-wing, authoritarian and insensitive English. The party emphasises the sort of issues that were until recently the preserve of single-issue campaigners. Both fracking and nuclear weapons are likely to be key features of negotiations with Labour if it seeks the support of the SNP’s Westminster MPs in some way on May 8th.

Such inter-party arrangements, either full coalitions or looser promises of support, look likely outcomes in Mr Curtice’s lottery (see chart 2). The Lib Dems look as if they could lose two dozen seats or more, and the SNP could make gains on the same scale. If UKIP and the Greens pick up a handful of seats, too, the number of seats held by the two main parties will shrink and the chances of a minority government, or a coalition of some sort, will rise. Political advisers and civil servants are dusting off histories of the period from 1976-79, the last in which Britain had a minority government. Political folklore has MPs at death’s door brought into the Commons on stretchers to vote.

Back then a minority government could seek a stronger mandate at any time by going to the polls. That is no longer possible. The Fixed-Term Parliaments Act, passed by the current coalition as a guarantee of its durability, requires the agreement of two-thirds of MPs to approve an immediate dissolution. The opposition may thus reject new elections if the timing does not suit it; that happened in Canada’s legislature, which uses the Westminster model, in 2008. Thus a weak minority government could persist for some time. The alternative worry is a government which is not inherently wobbly but which the ever more grotesque distortions of FPTP strip of legitimacy. Polling suggests that UKIP could come third in share of the vote and sixth in number of seats; the SNP, on the other hand, could come sixth in share of the vote, third in number of seats and get to choose the government. The Greens and UKIP could together obtain a quarter of votes but only 1% of the seats. Labour could win more seats than the Conservatives with many fewer votes. It is indeed conceivable, though unlikely, that Labour could win an absolute majority with less than 30% of the vote. An added complication is the House of Lords. In Labour and Lib Dem circles the talk is of turning it into a senate elected by PR of some sort. That might to some extent mollify small parties; but by highlighting the unrepresentative nature of the Commons it might well also make that chamber’s legitimacy harder to defend.

Britain may muddle along, as it has done when its electoral system has creaked in the past. Weak governments in the 1970s gave way to more than a decade of handsome Tory majorities as FPTP squashed the attempts of the Liberals, allied to the Labour absconders in the Social Democratic Party, to split the two-party system. (In the 1983 election Labour, with 28% of the vote, got 209 seats; the SDP-Liberal alliance, with 25%, got 23.) People seeing their votes for small parties wasted and no likelihood of that changing might return to Labour or the Tories—one of which might yet come up with a leader and programme that appeals both to its ideologically hardcore members and to centrist voters. And it is worth remembering that though it favours a two-party system, FPTP has in the past allowed the identities of those parties to change, with Labour supplanting the Liberals. Perhaps, after a period of turbulence and realignment, a new two-party configuration will emerge and stable majority governments will return. Duverger’s law is strong. But it is also possible to imagine Britain responding to its great political fragmentation by giving up, or modifying, FPTP. The Lib Dems, a merger of the Liberals and the SDP, have steadfastly favoured PR (and after the 1980s who could blame them?). The Greens do, too, and so do some in UKIP—including Nigel Farage, its leader. It is easy for small parties to favour a reform that gets them more seats. It is more notable that the SNP, which looks likely to do very well out of FPTP in May, also favours PR at Westminster. And so does a substantial body of opinion in Labour.

Wellington calling

Only the Conservative Party is resolutely anti-PR. The party is conservative by temperament as well as name. It sees itself as the “natural party of government” and finds it inconceivable that in any two-party system it will long be out of power. Forced by the Lib Dems to hold a referendum on an uninspiring modification of FPTP called “alternative vote” as a coalition dowry, nearly all Tories campaigned for a “No”. Yet the party’s interests are shifting.

The current system is punishing Tory voters for being increasingly concentrated in rural and wealthy parts of the country; it is that concentration which makes it possible for Labour to get more seats than the Tories with fewer votes. Some senior Conservatives—including, it is said, the prime minister—favour introducing PR in local elections to establish a presence for the party in parts of the country where it lacks local councillors, let alone MPs. (It has no representatives on the councils of Manchester, Liverpool, Sheffield or Newcastle.) Mr Bale, an expert on the party’s recent history, says that the sight of UKIP taking many votes from the party yet failing to translate them into a largely supportive bloc of right-wing seats in Parliament might finally make first-past-the-post intolerable. And if enough people across the major parties favour it, reform will become possible, even inevitable.

Even if the Conservatives do not change their stance, grossly disproportionate election results could still force the issue. That was the case in New Zealand in 1993 when, after years in which the two main parties had lost a lot of votes but only a few seats to smaller outfits under FPTP, the public voted for reform in a referendum. Admittedly this was in part because of an earlier non-binding referendum which the then prime minister had offered by accident (he misread his notes in an interview and chose not to correct himself). But chance always has a role to play.

The fact that an FPTP system like that of New Zealand before the 1990s—so majoritarian people called it “more Westminster than Westminster”—gave way fairly easily to a form of PR suggests the same could happen in Britain, too. Indeed, such systems are already in use in the London and Welsh assemblies as well as Holyrood.

The contrast between the architecture of Holyrood and that of Westminster illustrates the differences between the two systems: one is rigidly divided, opposing winners and losers; the other offers a spread of possibilities for compromise and deal-making. Scotland’s legislators speak from individual desks in a horseshoe (they tend to sit in groups, but can take any seat in the chamber if they want) in an airy complex that feels like a modern airport: all bright, wide galleries full of seating.

The architectural parallel has one further dimension. Like Britain’s electoral system, the Palace of Westminster was completed in the second half of the 19th century, survived occasional blows through the 20th century, and is poorly suited to today’s politics. Like the electoral system, it is close to falling to bits. A drastic restoration is planned for the next parliamentary term; some or all MPs may have to move out. For Britain’s constitutional reformists—which include this newspaper—this presents a golden opportunity to fix both the physical and electoral architecture of British politics. The edifice may survive the next parliament, and even the one after that. But without drastic renovation it could easily collapse.