What Would It Take for Jeremy Corbyn to Win the U.K. Election?

Prime Minister Theresa May warned voters that if her Conservative Party loses just six seats in next week’s U.K. election, Jeremy Corbyn could become head of a coalition government.

We decided to go a step further. Using the seat calculator in Bloomberg’s U.K. Election Tracker, we can find out what would need to happen on June 8 to deliver an upset on election night.

Short answer: It’s possible, but still unlikely. For Labour to win a majority, the party would need perhaps a 10-point lead; requiring a swing of 8 points since the 2015 election. Since World War II only Tony Blair has pulled off such a feat, on his way to a 1997 Labour landslide.

What’s undeniable is that May’s once-unassailable lead has shrunk from as much as 24 points at the campaign’s inception to as little as 5 points closer to the finish line. Polls in the U.K. have been battered by high-profile misses, most recently the Brexit referendum, which is why we’re looking into these improbable outcomes as public opinion vacillates. YouGov Plc came out with a new model on Tuesday that suggested the Tories may even lose their majority.

QuickTake Q&A: What Polling Swings Mean for the U.K. Election

May was looking at a landslide at the start of the campaign. Now she risks doing worse than former premier David Cameron, who won in 2015 with a 6.5-point advantage over Labour.

We have taken the polling data and plugged them into a seat calculator to see what it would mean for Labour. Taking the poll that's most favorable to Corbyn from last week, Labour would snatch about seven seats from the Conservatives, who would still have a narrow majority in the House of Commons and perhaps 90 seats more than Labour.

A further 1-point swing to Labour could take us into a hung parliament, the scenario May was conjuring up in a bid to scare voters  on the campaign trail.

While the Tories would still be the largest party, with around 75 seats more than Labour, May would be just short of a majority in the Commons. But even with the support of the Liberal Democrats, the Scottish National Party, Plaid Cymru and the Greens — described as the “coalition of chaos” by May — Corbyn would struggle to match May in terms of seats.

If Labour can tie with the Tories on 40 percent — a level of support the party has only reached twice since 1970 — Corbyn might just be able to cobble together a bare majority in the lower house. But he would need help from the other anti-Tory groups, and possibly Northern Ireland’s Social Democratic and Labour Party.

Turning the tables on the Tories and emerging with a 5-point lead would still leave Labour short of an overall majority in the Commons, swing calculations suggest. That’s because the loss of dozens of Scottish districts to the SNP in 2015 has hurt Labour the most.

Our calculator suggests Corbyn would be about 20 seats ahead of the Tories in such an instance, but still some 30 short of the Commons winning post.

The numbers suggest Corbyn has an uphill battle to seize the keys to 10 Downing Street, even if Labour’s polling numbers improve over the next eight days.