What would it take for Labour's Jeremy Corbyn to actually win the British election?

UK Prime Minister Theresa May has warned voters that if her Conservative Party loses just six seats in next week’s UK election, Jeremy Corbyn could become head of a coalition government. But how likely would it be that June 8 election night delivers such an upset? Short answer: It’s possible, but highly 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 24 points at the campaign’s inception to as little as 5 points closer to the finish line. Polls in the UK have been battered by high-profile misses, most recently the Brexit referendum, which is why even an improbable outcome demands scrutiny as public opinion vacillates. A total of seven polls carried out since the May 22 Manchester attack have shown May’s lead over the Labour Party narrowing. A poll conducted by Survation for ITV’s Good Morning Britain programme showed May’s lead had dropped to 6 percentage points from 9 points a week ago and 18 points two weeks ago. An ICM poll for the Guardian showed May with a 12-point lead - enough for a big majority of around 100 but down two points from last week and a far cry from the record 22-point lead earlier this month. “Three weeks ago this was the easiest election to call in history,” said Martin Boon, ICM’s director. “But since the manifestos were launched, there’s been a rapid tumbling in the gap between the Conservatives and Labour,” he said, referring to the pre-election pledges of the main parties. May was once looking at a landslide, and now she risks doing worse than former PM David Cameron, who won in 2015 with a 6.5-point advantage over Labour. YouGov polling figures from Thursday that were the most favourable to Corbyn were plugged into a Bloomberg seat calculator. The result: 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 Britain into a hung parliament, the scenario May was alluding to 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 per cent — 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 2010 has hurt Labour the most. Bloomberg’s 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 faces an uphill battle to seize the keys to 10 Downing Street, even if Labour’s polling numbers improve in the run up to June 8. May called the snap election in a bid to strengthen her hand in negotiations on Britain’s exit from the European Union, to win more time to deal with the impact of the divorce and to strengthen her grip on the Conservative Party. But unless she handsomely beats the 12-seat majority her predecessor Cameron won in 2015, her electoral gamble will be seen to have failed, and her authority could be undermined just as she enters formal Brexit negotiations. Additional reporting by Reuters