At every stage of Jeremy Corbyn’s rise, the British left has shocked itself. As the 2015 Labour leadership contest started up, we braced for a sharp rightward shift in the party, with seemingly no hope of a left wing challenger reaching the ballot. Then Corbyn won. This week, YouGov is projecting a hung parliament, with other polls putting Labour on up to 39 per cent of the vote. Two weeks ago we had been preparing to declare any improvement on Ed Miliband’s 31 per cent vote share a good result, even while the Tories enjoyed a substantially larger majority.

After two years in which the parliamentary party has been openly at war with the leadership, making modest improvements in its share of the popular vote could still count as a good result for Corbyn’s Labour. The grim reality of the Ukip collapse – which was the real story behind the Tories’ gains in the local elections in May – is that Labour could do better in this election than it did in 2005 (when it got 35 per cent) and still lose seats. But if youth turnout is high and recent polling trends are broadly accurate, Labour could be on course to do something far more significant than holding their ground.

For Labour to be doing even this well is a vindication of a very simple mantra - that radical social and economic policy, clearly articulated, is the party’s only route back to power. In early April, the opposition was split from top to bottom by Brexit, and had just lost a by-election to a governing party for the first time since 1982. Even the Corbynite base of the party, having endured its own internal strife in Momentum, was beginning to look tired and demoralised. But by calling a snap election, Theresa May released Corbyn from the despatch box and created space for the left to do the one thing that could bring it back from the edge.

The extent to which Labour has managed to cut through with its big manifesto pledges – progressive taxation, a real living wage, free education, free school meals, free childcare – has confounded commentators. As the election was called, I wrote that “the natural instinct for the Labour leader to take a series of defensive stances on immigration and Brexit, and move the conversation on to something else […] would be suicide”.

Evidently, I was wrong. Labour’s "change the subject" strategy is working. Brexit is undoubtedly still the main issue, but it is not big enough to carry the election among the sections of the electorate which matter. The parties which have bet most on representing one side or another of the Brexit divide – the Lib Dems and Ukip – are both having an awful campaign. Social care, the NHS and education become so central that they are drowning out Labour’s weak spots - flag, military and monarchy. The press spent years painting Corbyn as an IRA sympathiser, but now the election is on the public don’t seem to care.

Corbyn’s campaign has coupled its aggressive policy strategy with an insurgent, anti-establishment tone. Gone is the “kinder, gentler politics” that struck a chord with his own party members. Instead, from the opening speech of the campaign, Corbyn has targeted the economic elite and provided a clear narrative on inequality and class. The result is that Labour looks set to avoid the catastrophe endured by the French Socialist Party (6.3 per cent of the vote) or the Dutch Labour Party (5.7 per cent of the vote) this year. As it stands, the blueprint for the survival of European social democracy will be a sharp turn to the left.

In the final days of the campaign, Theresa May will double down on Brexit and immigration in the hope of defining both the election and her opponents on her terrain. In April, she would have expected to be doing so in the knowledge that her lead was unassailable. Now she must do so in the hope that narrowing polls will mobilise the Tory base. If this works, the polls could go right back to where they were in April. If it doesn’t anything is possible. It’s the hope that kills you, they say.