The closing scene of the Werner Herzog movie Aguirre, The Wrath of God is a gift for any writer in search of a metaphor. It is a study in futile ambition and abject failure. This week, a phalanx of Jeremy Corbyn supporters brought it immediately to mind.

In the 1972 classic, the famously unhinged actor Klaus Kinski plays Don Lope de Aguirre, a conquistador fiercely determined to discover the mythical City of Gold. He is relentless; willing to brutally discard the disloyal or those who lack his maniacal desire

He ends up on a crumbling river raft, surrounded by a replacement crew of excitable monkeys. As the credits roll his hubris is undimmed.

You probably know where this is going.

Countdown star Rachel Riley has been tweeting her concerns about antisemitism over the past few days. In return she has received an extraordinary volley of abuse from Labour voices who consider her comments an attempt to undermine the party leadership.

Riley has not backed down. She has since said she fears Corbyn has given “a legitimate voice to Holocaust denial”. Lifelong Labour supporter and Riley’s Countdown co-star Nick Hewer, has ditched the party in the aftermath.

Beyond the antisemitism row, Labour MPs have become used to seeing careers dedicated to progressive politics come under attack for a failure to share in Corbyn’s purity of vision.

And it has gone further. We published a piece last week from a journalist who had voted Labour all of her life, but who found Corbyn’s approach to Brexit too painful to bear. She jumped ship to the Lib Dems and is now fighting to secure a new referendum.

It felt like part of a plausible trend. It would be no great surprise if hard-Remain Labour voters start to accept that Corbyn’s sympathies lie elsewhere. A People’s Vote poll with a sample size of 25,000 claimed Labour could fall to third among voters if Corbyn definitively backs Brexit.

The author of the piece, Liz Jarvis, had done what relatively few people in Britain ever consider: break free of their hardwired political habits. But that wasn’t what sparked a rash of irate responses on social media from Corbyn loyalists.

The key objection was that Jarvis, a journalist, had sometimes written for The Sun. Worse, went the argument, she now works for a travel publication on the fringes of the “luxury’’ sector. (I’m not going to tag her employer here).

“SEE!?” went the gleeful fury. “SHE CAN’T BE REAL LABOUR. She’s pretending! Good riddance to bad rubbish!” (I’m paraphrasing).

But this wasn’t just a handful of aggressive tweets and the odd spluttering comment under the article. Hundreds shared one Twitter user’s revelation that someone writing in a newspaper was a... err… “journalist” (spoiler: it’s not unknown). The outrage made it into The Canary, a website which acts as a mouthpiece for the hard left in the Labour Party and beyond. The implication was that this was not a voter who deserved to support Labour.

I know a few people who have worked for The Sun. At least two of them vote Labour. What should I tell them? I know at least one person who worked for the Daily Mirror and is definitely a Tory (I confess I never asked). Do they cancel one of the others out? I once worked for a bank. Am I allowed to carry on voting Labour?

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I’m interested where the cut-off point is: how in tune with the Labour leadership do your life choices have to be?

There must be room in the Labour Party for people who simply prefer collectivism over individualism, and who want a more equal society “for the many, not the few”, but who just go about their lives as best they can. They might shop at retailers with questionable supply chains; fail to join their union; they might have an uncomplicated view on antisemitism; or despise allotments.

You can maybe understand the tribalism at party level. Team Corbyn has grown used to firefighting parliamentary insurgencies against their earnest, fragile leader.

And if I deploy every ounce of empathy, I can see the flawed logic behind the anger when a well-liked famous person – like Rachel Riley – offers a measured takedown of failures in the party leadership.

But voters?

The Labour plan on Brexit is to somehow finagle a general election from Theresa May’s calamitous wreckage. That’s not ridiculous. It’s looking more and more likely that a public vote of some kind is the only credible solution at the end of each avenue.

But when a general election does come around, Labour will need more than a coalition of hardcore campaigners to reach electoral El Dorado.