Before more absurd hyperbole took over – Tony Blair comparing Jeremy Corbyn this weekend to Donald Trump and Marine Le Pen – the prevailing rhetoric was that Labour was in danger of returning to its comfort zone. From the point of view of a loyalist on the soft left of the party, it hasn’t felt like that. I joined just after the Tony Benn/Denis Healey deputy leadership contest in 1981, and so have never had to confront the prospect of the party leadership moving seriously leftwards. Suddenly, completely unexpectedly, Corbyn’s rise made it feel like it was happening. I found that heady and inspiring, but not comfortable at all.

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Suddenly, those of us who have brayed from the sidelines – about dropping Trident, de-privatising the railways, celebrating rather than unravelling multicultural Britain, and doing something serious about income inequality – have had to confront some serious arguments. We have – for the first time in decades – the giddy prospect of our most cherished policies becoming the core of Labour’s programme. But we also face the risk that the forces of opposition are correct: that these policies are electoral anathema, or unworkable, or both.

Rightly or wrongly, Labour was seen as running the general election on the most leftwing programme since the 1980s, resulting in an unmitigated disaster or trainwreck or catastrophe or meltdown. Gordon Brown said Labour supporters were grieving, as if the party were dead.

Well, Labour certainly lost. But the perceived scale of the defeat was exaggerated by the false opinion polls and Labour’s collapse in Scotland. The party gained over a million extra votes in England. Overall, it gained only 200,000 fewer votes than in 2005, when it won an overall majority. Having lost nearly 4m Labour votes under the supposedly infallible Tony Blair, 2015 was the first election since 1997 in which Labour increased its vote. It wasn’t the result we wanted or were persuaded might happen. But nor was it a tsunami.

Did Labour perform disappointingly because its manifesto was perceived as too leftwing, the lesson of 1983? Clearly, it didn’t gain enough Conservative votes in England. But unlike in 1983 – shortly after the party had split to its right – it also lost shedloads of votes to parties positioned to its left. The SNP, Plaid Cymru and the Greens together tripled their 2010 vote, to nearly 3m. Indeed, if you add the votes for those anti-austerity parties to Labour’s, you beat the Conservatives by more than 800,000.

Unlike in 1983, 6.6 million people voted for parties opposed to the Westminster status quo

That begs the question of the nearly 4m-strong Ukip vote, particularly in the 44 seats in which it came second to Labour (and the 2.4m votes for the Liberal Democrats). There was not a progressive majority in the 2015 general election. But there was a spectacular progressive swing in parts of the kingdom that ate into Labour’s vote. In addition, in many Labour places an angry, oppositional party took votes away from Labour, but also from its traditional opponents (where Ukip came second, knocking Conservatives and/or Liberal Democrats into third). Unlike in 1983, 6.6 million people voted for parties opposed to the Westminster status quo. A fragmenting electorate had abandoned the centre-ground comfort zone well before Corbyn threw his cap into the ring.

So what would a Corbyn-led Labour party look like? For people like me, it’s a relief that hitherto no-go areas for mainstream Labour politicians (such as not renewing Trident) are no longer beyond the pale. But, as Blair pointed out, much of Corbyn’s economic platform consists of defending New Labour programmes from Conservative attack. Putting the massively subsidised railways into public ownership is merely a reflection of economic reality, and public control of energy industry pricing was one of the most popular elements of Labour’s last manifesto. In 2015 the Conservatives created a malign image of welfare state beneficiaries (excluding pensioners) that in effectunited the middle with the rich against the poor. What Blair refused to do, and Ed Miliband failed to do, was to unite the middle with the poor against the rich.

But there are other strands of thought that were pursued over the past five years only to slip off the radar as the election approached. There was a swath of devolutionary, bottom-up democratising thinking, notably associated with Jon Cruddas’s policy review and the Compass group, that was sidelined by panicky pre-election offer-shrinkage, and could form the basis of a democratic transformation.

And then there is the politics of left activism, like the Stop the War coalition, which organised the vast 2003 anti-Iraq-war demonstration, and of which Corbyn is chair. There are so-called hard-left groups involved in Stop the War. But its core ambitions are liberal and plural: peace, disarmament, internationalism, a consistent opposition to the demonisation of British Muslims, and the defence of human rights, abroad and here. One of the many casualties of the war on terror was New Labour’s traditional commitment to civil liberties, as the government that gave us the Human Rights Act moved on to control orders and 28-day detention.

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Corbyn has always supported LGBT rights, and was one of the earliest parliamentary supporters of gay marriage. For many young people some of his other ideas are new. But for me he promises a rejuvenation of the economic interventionism and social libertarianism that brought about Labour’s greatest achievements – the welfare state in the 40s, the social reforms of the 60s, and – yes – the minimum wage, civil partnerships and Equality Act of the Blair/Brown years. A Corbyn victory could open up the possibility of an alliance, within and beyond the Labour party, between post-austerity economic thinking, democratic and community renewal, and social and civil libertarianism, and thereby regenerate the social-democratic project.

Finally, for the first time in my life, a new Labour leader might be elected not by a deal or a campaign, but by a movement. What are we about, if not that?