In an election that opinion polls predicted was too close to call, the outcome was suddenly and startlingly clear. David Cameron is back in Downing Street and this time as prime minister of a Conservative majority government, his party having taken many seats from its former coalition partners, the Liberal Democrats. Cameron’s victory comes as a huge surprise, after opinion polls throughout the campaign put his Conservatives and their Labour rivals neck-and-neck. All indications pointed to a hung parliament, with no party winning an overall majority. Why did the Conservatives do better than expected? Six reasons are explained below.

First, the Tories benefited from the collapse of the Labour vote in Scotland. Labour held on to only one of its former 41 parliamentary seats out of Scotland’s 59. Despite losing the referendum on Scottish independence last September, the Scottish Nationalist Party (SNP) won 56 seats, a staggering increase from just six before the election. Capitalizing on widespread Scottish voter antipathy toward the Cameron-led coalition, the SNP skillfully positioned itself as the natural alternative to the Tories in Scotland. Hoping to deprive Labour of electoral support, the Conservatives and their friends in the press were only too happy to encourage the SNP surge.

Second, it wasn’t just in Scotland that Labour failed to connect with voters. Outside London, Labour made few significant gains in England. Despite confounding his critics and performing better in election debates than expected, Labour leader Ed Miliband ultimately couldn’t convince voters that he was better able to lead Britain than Cameron. Miliband partly suffered from carefully coordinated attacks in the Tory media, painting him alternatively as “Red Ed” — the socialist scourge who would allow the SNP to dismantle the United Kingdom — or as an incompetent nerd, literally lacking the skill to eat a bacon sandwich.

But Miliband and his inner circle also bear responsibility for Labour’s defeat. By accepting the Conservative’s borrowing plans, Labour allowed the Tories to make paying down Britain’s deficit a key election issue. Rather than challenge the assumption that borrowing is the biggest bogyman facing the British economy, Labour accepted the Tories’ economic narrative.

Miliband further failed to dispel the myth that overspending by the last Labour government is the cause of Britain’s current debts.

As Nobel Prize-winning economist Paul Krugman points out, bank bailouts necessitated by the 2008 global financial crisis, coupled with five years of under-investment by a Conservative-led coalition obsessed with austerity, did more to harm the British economy than spending on public services by the Labour governments of Tony Blair and Gordon Brown.

By promising a form of “austerity lite” that would allow Labour to pay back the deficit, albeit at a slower rate than the Conservatives, Miliband opened his party to the charge of being a watered-down version of the Tories.

In reality, at this election Labour offered its most distinct platform from the Tories since 1992, but failed in communicating this message. By contrast, in Scotland the SNP articulated a simple-to-digest, progressive alternative to the Conservatives, offering an end to austerity and the dismantling of Britain’s nuclear weapons system, Trident.

Third, the Conservatives gained from the implosion of their former coalition partners, the Liberal Democrats. The Lib Dems usually benefit from tactical voting by both Labour and Conservative supporters. But at this election the Lib Dems were abandoned by left-leaning voters, angry at the party for propping up five years of Conservative-led government.

Plummeting from 57 to just eight seats, voters pummeled the Lib Dems for openly reneging on their 2010 election promises and endorsing Tory policies, such as backing a tripling of university tuition fees, despite a pledge to abolish them. If Cameron is the Dorian Grey of British politics, Lib Dem leader Nick Clegg has become the portrait in the Tory leader’s attic, withering as his Conservative counterpart remains fresh-faced and unscathed.

Fourth, the right-wing, anti-EU UK Independence Party (UKIP) failed to eat into the Conservative vote as much as expected. Despite gaining 12.6 percent of the popular vote, UKIP won only one seat. Many traditionally Tory voters who flirted with UKIP appear to have come back to Cameron at the last minute, perhaps convinced by the Conservative leader’s mantra “vote UKIP, get Miliband.”

Fifth, pollsters may have underestimated what is known as “the shy Tory effect.” Those intending to vote for the Conservatives—sometimes called the Nasty Party—are embarrassed to admit their true affiliation to pollsters. Shy Tories are commonly seen as the cause of Britain’s last significant electoral upset in 1992, when Conservative John Major won a surprise victory against Labour’s Neil Kinnock in an election with many similarities to 2015.

Finally the Conservatives were helped by biases in Britain’s “first past the post” electoral system that disproportionately distributes seats to the two main parties at the expense of their smaller rivals. Cameron won a majority of seats on the back of a 36.9 percent vote share, while Labour won 35.7 percent of seats with just 30.5 percent of the vote. In contrast, the Lib Dems won only 1.2 percent of seats compared to 7.8 percent of votes.

Biases in the electoral system favoring the Conservatives will likely deepen during this parliament. Tory plans to redraw district boundaries and to reduce the number of parliamentary seats from 650 to 600 will make it even harder for Labour to win a majority or to form a coalition with smaller left-of-center parties. The abolition of seats will mainly affect Scotland and Wales, where voting district populations are smaller than in England, and where the Conservatives hold few seats.

There is no doubt that this election belongs to Cameron. But his honeymoon may prove short. With a majority of fewer than 10, Cameron will have to work hard at maintaining unity within his party. A referendum on Britain’s continued membership of the EU, promised for 2017, could easily split the Conservative Party, as the issue of Europe did for Major’s government in the mid-1990s. Although Cameron and his business backers would prefer to see Britain remain in a reformed EU, many Eurosceptic Conservative backbenchers would prefer Britain’s exit.

Furthermore, the SNP’s landslide in Scotland provides a clear mandate for greater devolution of powers from London to Edinburgh, and possibly another referendum on independence down the road. Devolving greater autonomy to the Scots will exacerbate already simmering regional divisions, which Cameron has stoked by playing on English indignation over perceived privileges granted to Scotland at the expense of their southern neighbors. Cameron could yet become the prime minister to preside over the breakup of two historic unions: a European Union containing the U.K., and a U.K. containing Scotland.

Tina Burrett is an assistant professor of political science at Sophia University, Tokyo.

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