Imagine for a second hordes of BNP, EDL and National Front members mounting a hostile takeover of the Conservative Party. Consider how they’d set about transforming the organisation from top to bottom.

Crazed fanatics would be swiftly installed in the leader’s office. Formerly genteel constituency party meetings would see polite and elderly blue-rinse Tories shouted down by shaven-headed thugs.

And Conservative frontbenchers would boast openly of consulting with racist organisations to decide foreign policy.

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'The lunatics' have taken over Labour, according to Simon Danczuk, the party's MP for Rochdale. Pictured, Labour leader Jeremy Corbyn at an anti-war rally in October 2012, (file picture)

It couldn’t happen, surely? It seems highly unlikely, as the Conservatives are too interested in being a party of government to allow it.

But the same chilling scenario is unfolding in the Labour Party right now. The only difference is that the fanatical ideologues who have seized power are at the other end of the political spectrum.

History tells us that extremist ideologies are dangerous whether they’re hard Left or hard Right. At some point the swivel-eyed lunacy on both sides meets with the same result.

Whether it’s communism or fascism, it always ends in deadly purges, misery and dictatorial madness.

That’s why Labour moderates are finally waking up to a nightmare that’s been slowly unfolding since the day Jeremy Corbyn was elected leader.

Tom Watson’s warning last week that entryists are trying to infiltrate Labour shows Corbyn’s not-so-secret plan has finally been rumbled.

Simon Danczuk, pictured, Labour MP for Rochdale, said 100 years of Labour Party history hangs in the balance now that Jeremy Corbyn is leader

Anyone who still sees the hard Left through a romantic prism of heroic struggles like those of the Tolpuddle Martyrs, Chartists and Jarrow marchers can no longer ignore the ugly reality.

Layer upon layer of warm, comforting sentiment is being peeled away to reveal spiteful thuggery and a repugnant philosophy.

There’s nothing edifying to see here. Whether it’s Corbyn supporters celebrating the hospitalisation of Labour MP Mike Gapes, the lynch mob mentality on social media, or threats and intimidation from pitch-fork-wielding revolutionaries in Momentum, the ‘new politics’ has long abandoned any pretence of decency.

And now that the tone of the ‘new politics’ has hardened, Jeremy Corbyn’s backing band, the Stop the War Coalition, are busy setting the mood music to a sickening new doctrine.

When they’re not playing down the crimes of fascist butchers IS and unbelievably comparing jihadis to the International Brigades that fought against fascists in the Spanish civil war, they’re blaming the French for terrorist atrocities in Paris and preventing Syrians from speaking at their rallies because they support a no-fly zone.

But their hate-the-West, blame-Britain-for-everything, apologia-for-fascism doesn’t stop there. Oh no.

‘Support for Bashar al-Assad’ flags flutter in the breeze at their demonstrations and they refuse to protest against Assad’s barrel-bombing of his own people.

They’ve compared Assad to Churchill, say they stand with Saddam Hussein, and find themselves in the company of the BNP in their support for Putin.

Boil down their confused philosophy and it amounts to little more than viewing Britain as a bigger threat than IS, Saddam and Putin combined.

Little wonder that even leftier-than- thou types such as Peter Tatchell and Caroline Lucas are walking away from this muddled and treacherous outfit.

But there’s one person who will never walk away and that’s their cheerleader-in-chief, Jeremy Corbyn.

As we saw last week, he’ll continue to robustly defend them at every turn. Because their values are his values – and he mistakenly thinks they are Labour values.

Mr Corbyn pictured leaving a Stop the War fundraiser where he made a speech on Friday night

It’s not just that he’s tragically wrong that’s so exasperating to many. It’s that the Left has such a rich history that Corbyn could draw from.

But instead of deriving inspiration from Robin Cook’s principled decency in his opposition to the Iraq War, or Clement Attlee’s instinctive grasp that patriotism ‘was the emotion of every free-thinking Briton’, Corbyn persists in dropping his bucket into a dry extremist well.

As the leader of a mass-membership political party that aspires to govern one of the greatest countries on earth, such behaviour is totally unacceptable.

Mr Corbyn, pictured second right, on the opposition front bench in Parliament with some of the shadow cabinet

You only had to listen to the resounding cheers that greeted Angela Eagle’s performance at Prime Minister’s Questions last week to know Labour MPs desperately want to beat a path out of the wilderness.

Jeremy is stretching the Labour Party to breaking point. And sooner or later something must give.

Labour’s always been a broad church but differences of opinion are now so great that unless Corbyn begins to build bridges with the vast majority of Labour MPs, it’s going to become obvious to the public that we’re two separate parties.

And once this becomes accepted public wisdom a split will be inevitable. Jeremy needs to realise what’s at stake here. More than 100 years of Labour history hangs in the balance.