It must have been the shortest political honeymoon ever. Barely had the landslide election of Jeremy Corbyn as Labour leader been announced than the backlash began in earnest. The 100-1 outsider might have pulled off the most extraordinary democratic leadership victory. But when it came to the political and media establishment, the usual niceties were dispensed with entirely.

Within minutes, the first of a string of Blairite resignations from shadow cabinet jobs they had not yet been offered had begun. The Conservatives issued bloodcurdling warnings about the threat posed to the security of the country and every family in the land. And the media campaign was raised to new levels of hysteria – with Corbyn and his allies depicted as deranged terrorist sympathisers.

One more notch on the propaganda dial and they’d be calling for the Labour leadership to be deported to internment camps in Caithness. The onslaught was expected. But the anti-democratic virulence of Britain’s tax-dodging media monopolists still has the capacity to take the breath away. It has also served to obscure the scale and significance of what has taken place.

The anti-austerity revolt has found its voice in Britain in an entirely unexpected way

There is no parallel for such a dramatic democratic upending of official politics in Britain. In three months Corbyn went from backbench obscurity to winning more than a quarter of a million votes, nearly 60% of the total, beating Tony Blair’s 57% when he was first elected leader in 1994 as well as eclipsing Blair’s support from individual members. Corbyn drew hundreds of thousands into the Labour party and reduced the Blairite candidate Liz Kendall to a humiliating 4.5%.

By any reckoning, Corbyn’s election and the movement that delivered it represent a political eruption of historic proportions. Whatever now happens, such a fundamental shift cannot simply be reversed. Eight years after economic crisis took hold of the western world, the anti-austerity revolt has found its voice in Britain in an entirely unexpected way. The political conformity entrenched during the years of unchallenged neoliberalism has been broken.

For the first time in decades, an unapologetic socialist is at the head of one of Britain’s two main parties. Meanwhile the Tory government is launching a legal assault on trade unions – on the right to strike, Labour’s funding and trade unionists’ civil liberties – that has been branded as Francoite by the Conservative MP David Davis. It’s an attack that is clearly aimed at destroying the labour movement as an effective political and industrial force.

The idea that this represents Tory colonisation of the “centre ground” is evidently absurd. Instead, politics is polarising in response to over a decade of falling living standards, rising insecurity and economic crisis. The media and political establishment has proved incapable of managing the intrusion of Corbyn’s democratic insurgency into what had seemed a well-insulated elite order. Media organisations that have for years called every major issue wrongly, from the war on terror to the economy, find themselves unable to deal with a movement that has overturned the rules of the game.

Corbyn has constructed a broad-based shadow cabinet that was widely predicted to be an impossibility

So instead they have seized on every mistake or gaffe, real or imagined, in step with the defeated Labour right, to try to derail the nascent Corbyn leadership. Those include everything from the lack of women in the traditionally most senior jobs – in the first cabinet or shadow cabinet ever to have a majority of women – to failing to sing the national anthem and leaving a broadcast media vacuum for opponents to fill.

The Labour leader has managed to see off the immediate threat by constructing a broad-based shadow cabinet that was widely predicted to be an impossibility. And the success of his crowdsourced debut at prime minister’s questions on Wednesday disarmed Cameron and stabilised, at least in the short term, a restive parliamentary party.

It’s scarcely surprising if the early days of Corbyn’s leadership have been chaotic. This is a spontaneous campaign that erupted out of nowhere, powered by grassroots volunteers across the country. The idea that it has been in the grip of a trade union machine is laughable to anyone who has seen it up close. Corbyn himself has no experience of such a leadership role and is inevitably on a steep learning curve.

If Jeremy Corbyn’s Labour is going to work, it has to communicate | Owen Jones Read more

But his evident lack of spin and professional political chicanery is of course part of his appeal. Corbyn’s most serious challenge, aside from a frenetically hostile media, will come from his own MPs. After years of New Labour control, the parliamentary Labour party was far to the right of the membership even before the influx of new recruits. Disinherited Blairites are already plotting to bring him down or, if they fail, in some cases to defect to the Conservatives.

Others can be expected to vote with the government, for example to authorise bombing Syria, against the new Labour leadership. New shadow cabinet members are already speaking out against the platform Corbyn was elected on, from his opposition to welfare cuts to his refusal to hand Cameron a blank cheque on EU membership renegotiation. Some of that can be swallowed as a new way of doing politics, so long as it doesn’t sink into incoherence.

But it also reflects an elemental clash between MPs, many of whom made it to Westminster courtesy of a centralised vetting operation, and a vastly expanded membership who want to take control of their own party. By giving rein to Labour’s democracy, the new leadership has the chance to change the balance of power. It will certainly be a rough ride. The media onslaught will continue. But if Corbyn’s supporters keep their heads, last Saturday can be the start of more far-reaching change: to break open the political system, put the alternative to austerity centre stage, and bring an end to Britain’s support for endless war.

To do that will need a powerful movement outside as well as inside parliament. The post-2008 reaction against austerity is now taking place in one country after another. The challenge is to translate that insurgency into political power. We don’t know how far Corbyn’s election can take Labour, or how long his leadership can survive. But one thing is clear: there will be no going back. It has already changed Labour, and British politics, for good.