JEREMY CORBYN’S triumph is cause for celebration for everyone who fights for a better world.

His victory was utterly overwhelming, with more than three times as many votes as runner-up Andy Burnham. And he topped the poll in every category — among registered supporters, affiliated supporters from the trade unions and full party members.

Corbyn’s mandate to lead the Labour Party is unshakeable.

And the enthusiasm he inspires wherever he goes — packing out halls at rallies in every corner of Britain over the past few months — shows that he is far and away the most popular politician in Britain today.

This has not stopped his detractors, from Labour peer Lord Soley through strike-breaking academic Tristram Hunt to failed mayoral candidate David Lammy, from talking down his prospects.

For too long, Labour has not been a party offering radical change to transform this country for the better but rather an alternative Establishment party happy to conduct “business as usual” in the British state — even though that has meant tolerating a Britain increasingly disfigured by inequality and injustice.

Many MPs are so wedded to the capitalist state that they will be reluctant to play the full and positive role in a Corbyn-led Labour Party that the new leader will want them to.

There are many others who have become convinced by years in the Westminster echo-chamber that the party has to tack to the right to win at elections, even though the evidence for this has always been weak and in recent years the growing constituency for parties offering radical change has been obvious.

We know that Corbyn will reach out to these members of his party and it will be all of our job to give Labour MPs the courage and confidence to support him.

His win is a tremendous step forward for the party and the movement. In itself, it changes Britain for the better.

It means the government will not be able to pursue its attacks on our public services, rights at work and living standards without encountering principled opposition on every front.

It makes it much less likely that this country will be dragooned into yet more disastrous acts of military aggression abroad.

But it is not everything — not by a long shot.

Whatever the naysayers claim, Jeremy Corbyn can win the next election and lead Labour back into government.

But we cannot underestimate the Herculean task ahead of us if we are to ensure that this happens.

Corbyn will be smeared and vilified by the monopoly media.

The challenge he, his politics and the movement he now leads poses to our rotten and corrupt political order is on a completely different scale from that of any recent Labour leader.

If we thought the attacks on Ed Miliband were disgraceful — and they were — we should brace ourselves for far, far worse.

The Tories will call him a threat to national security — they’re already doing so — and step up their demonisation of the poor, the sick and the disabled to win support for savage spending cuts.

And if yesterday’s string of shadow cabinet resignations is anything to go by, some in Labour will need some gentle pressure exerted on them to stop them undermining their own party.

That makes it essential that as a movement we maintain the momentum of recent weeks and stay united around Jeremy.

Defeating Tory lies on the streets and ensuring that his message is heard loud and clear in every part of these islands.

Defence Secretary Michael Fallon said yesterday: “This is a very serious moment for our country.”

It is indeed. The best chance for real change in generations. We as a movement must seize it with both hands.

Oh, and — congratulations, Jeremy. We knew you could do it!