WHO remembers the summer of 2015, when what first seemed impossible somehow became inevitable?

When Jeremy Corbyn agreed to stand for the Labour leadership, nobody — including the candidate himself — thought he’d win, or probably even get on the ballot.

But good luck saw him reach the ridiculously high nomination threshold a minute before deadline — and then, given the chance to vote for clear socialist values, Labour members did so in spades.

The summer’s slogan: “Jez we can!” summed up the spirit of hope and change as hundreds of thousands of people joined Labour or paid £3 for a say in the left’s future.

And although the Corbynista movement seemed to come from nowhere, it was just the latest manifestation of a protest culture stretching back from the People’s Assembly and UK Uncut to Stop the War and anti-globalisation in the 2000s, environmental direct action in the ’90s and beyond.

Led by the Labour left and fuelled by trade-union power, this new movement soon became unstoppable.

Odds that started at 200/1 came crashing down after Corbyn made the ballot on June 15 — from 100/1 that morning to 50/1 after hitting the midday deadline, then 33/1 as bets poured in all afternoon, falling to 25/1 by the evening.

It wasn’t until August that he became the clear favourite — which bookmakers William Hill called “the biggest price fall in political betting history” — while Corbyn-fever spread across the country with record-breaking rallies, a regular feature of his campaign.

Of course, the media demonised him relentlessly and pundits insisted he had no chance, but Jez still won with a landslide 60 per cent of the vote.

Cut to present day. We’re two weeks from a general election and the bookies have already slashed their odds against Corbyn taking the top job.

Two new polls from YouGov and Survation show that the Tory lead has halved in just a week — prompting New Labour spin doctor and arch Corbyn critic Alastair Campbell to tweet that the Tories are “eminently beatable.”

And while few people had even heard of Corbyn back in 2015 and his campaign was mainly staffed by volunteers working on a shoestring budget, he now has a powerful party machine mostly at his command, amplifying his anti-Establishment message as he hits the campaign trail for the third year running — although this time he’s standing for leader of the whole country.

As Labour surges in the polls, Corbynmania is sweeping the nation on a scale never seen before — just watch the 20,000 revellers at Saturday’s Wirral Live festival chanting: “Oh Jeremy Corbyn!” after his surprise stage appearance.

It was never meant to get this far. The plan was to oust Corbyn before any general election — in fact that was the pretext for last summer’s “chicken coup.”

When shadow cabinet members started resigning on June 26, deputy leader Tom Watson refused to back Corbyn, instead insisting: “It’s very clear to me that we are heading for an early general election and the Labour Party must be ready to form a government.”

Even though both the coup attempt and resulting leadership contest failed to dislodge Corbyn, the plotters thought they still had enough time to try again after Theresa May promised she wouldn’t hold a general election until 2020.

Like so many Tory promises, it was a lie but the fact that Corbyn will be on next month’s prime ministerial ballot is itself a miracle on the scale of June 2015.

Can he win three in a row? Of course — with the help of left-leaning youngsters. “If 30 per cent more people under 25 vote, the Tories could lose the election,” according to the i newspaper, and that’s without any further shift in public opinion.

Labour doesn’t need to win a majority, or even more seats than the Tories, to claim victory. As May tweeted on Saturday: “If I lose just six seats I will lose this election” — a far cry from the landslide first predicted by most pundits.

And if public opinion continues to move in Labour’s direction, it will neutralise the “Ukip effect” currently bolstering Tory support.

Corbyn’s policies are wildly popular, with 65 per cent of voters in favour of higher taxes for those earning above £80,000, compared with 23 per cent opposed, according to pollsters ComRes.

When it comes to banning zero-hours contracts, the numbers are 71 per cent for, 16 per cent against. And a whopping 78 per cent don’t want to see the return of fox hunting, with just 12 per cent backing May’s bloodsoaked signature policy.

The i is right — young people hold the key to this election. Sunday’s YouGov poll, which has Labour up four points to 35 per cent and the Tories down five to 44, shows the reds ahead among 18-24 year-olds by 57 per cent to 24, up from 49 to 27 last week.

Even among the much larger 25-49 year-old category, it’s still leading 46:30, up from 39:36 a week ago.

But the situation is reversed among older voters. Labour trails 29:50 with those aged 50-64, dropping to a dire 18:68 among people aged 65 and above — although the Tories have lost ground in both groups.

The problem is that youngsters are traditionally far less likely to vote. Only an estimated 43 per cent of 18-24 year-olds cast a ballot in 2015, while this soared to 78 per cent among the 65 and olders.

But that can change. Contrast Labour’s pledge to end university tuition fees immediately with the Tories’ plan to means test pensioners’ winter fuel allowance to understand the direction of travel, or May’s manifesto U-turn over the dementia tax — an unprecedented move she bizarrely blamed on “fake claims” by Corbyn.

Over a million 18-24 year-olds have registered to vote since this election was called — including a phenomenal 246,000 on Monday, the final day to sign up — out of almost three million total new registrations.

Many of them have been inspired by the stream of celebrities standing up for Corbyn. Big-hitters from the popular grime musical genre such as Stormzy and Novelist are backing Labour, with Jez meeting leading light Jme recently to snapchat about voter registration.

Endorsements from fellow musicians David Gilmour and Lily Allen appeal to different demographics, as do those from Noam Chomsky and even Hollywood legend Danny DeVito who tweeted last week: “UK you’ve got the guy,” urging followers to “vote for Jeremy Corbyn” and “show us how it’s done!”

Brexit may also be drawing young people into Labour’s camp. It’s estimated that 18-24 year-olds voted Remain by a factor of over 2:1 — and they’re now facing a choice between a Labour Brexit, which will basically keep the things they like about EU membership (human rights and study-abroad schemes such as Erasmus) while ditching what they don’t (the neoliberal agenda), and a Tory plan that promises the opposite.

Indeed, Labour has doubled its lead among all Remainers to 24 points (49:25) from last week’s 12 points (41:29), according to YouGov, while significant numbers of Leavers are also now deserting the Tories.

May is clearly panicking that her big election gamble has backfired, so expect the personal attacks on Corbyn to escalate over the next fortnight. The Sun is rerunning its “terrorist sympathiser” smears, which may have more impact after Monday night’s Manchester Arena atrocity.

But hubris has always been the Tories’ undoing, so tune out the defeatism and use every day left until June 8 to campaign in any way you can.

It’s time for #JezWeCan part III — the conclusion. Summoning the spirit of summer ’15 could see Corbyn’s democratic revolution finally become a reality — but if you think the media attacks on him are bad now, just watch what happens when he walks into No 10.

• Chat to Charley on Twitter: @charleyallan.