Days after Jeremy Corbyn won the 2015 Labour leadership election, party chiefs turned their attention to making this one-time joke candidate a credible contender to be Prime Minister.

Staff were hired and office space was filled. PR strategies were discussed and policy was devised. Efforts were even made (with mixed success) to persuade the scruffy allotment-holder to put on a smarter suit and do up his tie. Behind the scenes, aides began attempting to airbrush from history some of the more embarrassing episodes from Corbyn’s 35 years on the hard-Left of British politics.

These included his dealings with Marxists, the IRA, various dodgy anti-Semites, and some Islamist groups — including his ‘friends’ Hamas and Hezbollah.

Efforts were made to clean up his Facebook page, where he had for several years been highly active.

Jeremy Corbyn is accused of being a member of a secret anti-Semitism Facebook group

In particular, Corbyn was removed from Palestine Live, a group on the social network dedicated to discussing the Middle East from an anti-Israeli perspective.

He’d been a member of the group since shortly after it launched in August 2013.

The founder, a brunette middle-aged actress, artist and Labour activist called Elleanne Green, was a long-standing contact with whom Corbyn had previously discussed poetry online.

The duo’s relationship was sufficiently close for him to leave an affectionate send-off when she posted that she was about to holiday in socialist Cuba in April 2015, declaring: ‘Have a wonderful time and record it all.’

Crucially, to those versed in such matters, Green had designed Palestine Live as a ‘secret’ Facebook group. That means it cannot be found using the website’s search function, and could only be joined by people invited by a senior existing member.

Although the group’s 3,000-odd members included an array of Corbyn’s friends and political allies, from hard-Left Labour MPs Chris Williamson and Clive Lewis, to the socialist former BBC2 Newsnight journalist Paul Mason, their identities were therefore kept secret.

When he was elected as leader of the Labour party Jeremy had his Facebook 'cleaned-up' by specialists which included being removed from anti-Semitic group Palestine Live

Neither did outsiders know that Corbyn’s son Seb, who works as a senior aide to Shadow Chancellor John McDonnell, was also among its ranks.

The ‘secret’ status also meant that the public was unable to access content posted to Palestine Live. This was of great importance to some contributors.

‘How safe is this group?’ asked one, Jackie Walker, shortly after it launched. (Ms Walker rose to be vice-chair of the Corbynista Momentum pressure group, no less.)

‘Very,’ replied Elleanne Green. ‘No one is allowed in who is not trusted. I am very, very careful. And it is a secret group.’

But that was then. Today, just over four years down the line, Palestine Live is no longer ‘secret’. Quite the reverse. Earlier this month, the group — along with a swathe of its prominent members — found itself at the centre of the explosive furore over anti-Semitism in Corbyn’s Labour Party, after being exposed as a cesspit of Holocaust denial and vile Nazi-style propaganda.

The group’s 3,000-odd members included an array of Corbyn’s friends and political allies, from hard-Left Labour MPs Chris Williamson and Clive Lewis (pictured)

This was the result of an anti-Semitism campaigner and blogger called David Collier infiltrating the group. He compiled a detailed report telling how members such as Walker — who is currently suspended from Labour over allegations of anti-Semitism — used it to share cranky material about Middle Eastern affairs.

Some of the more sinister contributors (who, remember, thought they were operating in secret) were caught describing Jews as ‘demons’. Others accused Israelis of harvesting the organs of Arab children, or posted links to the rantings of white supremacists, including the leader of the Ku Klux Klan.

Several more used the group to promote ugly conspiracy theories, or share fake news articles suggesting that the number of deaths at Auschwitz had been exaggerated.

In an exhaustive 290-page report, Collier not only detailed this — his analysis suggests that 53 per cent of the contributors to Palestine Live were confirmed anti-Semites — but also uncovered the fact that Corbyn was an active member when such content was being shared on a daily basis.

Neither did outsiders know that Corbyn’s son Seb, (right) who works as a senior aide to Shadow Chancellor John McDonnell, was also among its ranks

The Labour leader posted comments on the site on a number of occasions — once, in October 2014, his remarks were published just below another referring to Jews as ‘Zios’, an anti-Semitic term of abuse (shorthand for Zionists) — and even helped leading members of Palestine Live invite a highly controversial speaker called Max Blumenthal to the Houses of Parliament.

Blumenthal, a Left-wing author critical of Israel, was, in 2013, accused by the Simon Wiesenthal Centre, a U.S. Jewish organisation, of being responsible for one of the ‘Top Ten anti-Semitic anti-Israel slurs’ made that year.

Top of the list was the supreme leader of Iran’s ‘genocidal threats against the Jewish state’.

Despite this, archived discussions found in the digital history on the Palestine Live page suggest that Corbyn agreed to help arrange his visit after being approached by Elleanne Green weeks earlier.

Though Corbyn was away from Parliament on the day itself, his office helped ‘look after’ arrangements to obtain a Parliamentary pass for Blumenthal, and booked the Attlee Suite at Portcullis House in Westminster for his speech.

Jeremy Corbyn meets with Rabbi Pinter (right) after delivering a speech on Labour's anti-Semitism inquiry findings at Savoy Place, London

Comments written on Palestine Live — which Corbyn failed to delete when leaving the group — further reveal that on the day Blumenthal was chaperoned by Jack Bond, an aide to the soon-to-be Labour leader who became his social media manager.

‘Kudos and thanks to the office of Jeremy Corbyn MP,’ declared Green, who is currently under investigation by Labour for anti-Semitism after being found to have used social media to share a story claiming that ‘Zionists’ are ‘killing children and stealing children to sell them on the black market’. Critics call this a modern re-working of the so-called ‘blood libel’, an age-old racist myth that Jews kidnap and murder the children of Christians to use their blood during religious rituals.

Green has also posted material claiming that Israeli intelligence services orchestrated both 9/11 and the Paris terror attacks as part of a secret plot to make Western governments interfere in the Middle East.

She once commented on Facebook that no ‘friend of Israel’ ought to be allowed to stand as an MP and shared a post suggesting the BBC employed ‘obnoxious Jews’ in order to goad opponents of Israel into anti-Semitism.

Corbyn’s association with such an individual is shocking. But given some of the horrific content on Palestine Live, it’s even harder to know exactly what he thought he was doing in her secret Facebook group.

Labour Party Conference at Exhibition Centre Liverpool in Liverpool

Such is the volume of bile shared on the site during Corbyn’s membership — which ran from April or May 2013 to late 2015 — that it’s impossible to detail more than a fraction of it. But it fell into three general categories.

One was Holocaust denial. In September 2013, a member of the group uploaded a link to a fake news story claiming, as he put it, that: ‘Official records from the International Red Cross prove the Holocaust was a fraud. Released records, sealed for years, show concentration camp death totals only 271,301.’

Corbyn’s friend Elleanne Green responded: ‘People should be allowed to discuss this rather than being silenced.’

In January 2015, a Palestine Live member called Andy Hopkins posted a video by David Duke, the leader of the Ku Klux Klan (KKK), claiming that the Holocaust was a hoax. ‘Perhapse [sic] if one asked some very basic questions they might learn the truth about the HOLOCAUST,’ he wrote.

A second regular theme involved wild assertions that Mossad, the Israeli security service, staged major terrorist incidents in order to increase tension between the Arab world and the West.

On the day in 2015 that Islamic terrorists murdered 12 members of staff at the satirical magazine Charlie Hebdo, for example, a member of the Facebook group called Allison Carmichael appeared to suggest the Israelis were behind the attack. ‘It looks like a MOSSAD-style hit was made today on the Paris offices of Charlie Hebdo.’

A year later, the group carried a link to a video titled ‘Did Israel’s Mossad do 9/11’, along with the comment: ‘Who knows? Anything is possible.’ Around the same time, someone called Simon Fox posted a video called ‘9/11 Israel and the Mossad investigated’.

The third anti-Semitic slur rampant on Palestine Live during Corbyn’s membership revolves around the suggestion that a sinister group of Jewish financiers secretly control the media and political establishment.

In August 2015, for example, a member called Tony Murphy complained of ‘Press manipulation by the Jewish community. They have such power and nobody seems to realise it. Very dangerous.’

In December 2014, a female member of a group called Sara Blaise posted another fake news article on this theme by the KKK’s David Duke claiming that the U.S. congress had ‘unanimously’ passed a ‘Bill confirming U.S. subservience to Israel’. She said the story, which was factually incorrect, ‘tastes like bile to me’.

In August 2014, Corbyn’s friend Elleanne Green shared a link to an article on a notorious racist website called ‘Political Vel Craft’ claiming that the Jewish Rothschild family are attempting to create a ‘New World Order’.

Then there were unalloyed racist insults.

In June 2015, a Palestine Live member called Tim Welsh declared: ‘It’s all over for the JewNazi.’ In September 2015, another contributor on the site wrote about ‘Jewish scum of the earth’.

A Pam Arnold, in September 2014, declared ‘these vile excrescences called Zionist jews should be wiped off the face of the earth’ before issuing a death threat against Jewish actress Maureen Lipman, whom she dubbed ‘unutterably vile, Zionist and Jewish Zionist especially to the core.’

Although these posts comprise just a small portion of the obnoxious material on Palestine Live, none of the site’s 3,000 members — including Corbyn and several Left-wing MPs — saw fit to point out the appalling nature of some of the material.

Neither did they contradict Holocaust denial, nor seek to point out that members of the group were sharing content produced by white supremacists.

To many within the Jewish community, this points to a wider malaise: that the hard-Left of Labour politics, where Jeremy Corbyn has spent his entire adult life, is so steeped in anti-Semitism that he’s simply unable to recognise it even when it’s staring him in the face.

Certainly his response to recent revelations has been a masterclass in obfuscation.

When David Collier’s report was originally published, Labour claimed that Corbyn had been added to Palestine Live without his knowledge or consent and had no active role in the group.

It was promptly pointed out that he had, in fact, written comments there. At which point the Labour leader’s office backtracked and said he had only been replying to messages.

That didn’t wash either, since Corbyn contributed to general content and, of course, had helped organise Max Blumenthal’s event in Parliament.

Corbyn therefore cravenly adopted a third position: that whatever his involvement with Palestine Live and its founder, he had never realised the site contained anti-Semitic material, so wasn’t guilty of wrongdoing.

‘I have never trawled through the whole group. I have never read all the messages on it. I have removed myself from it,’ he said. ‘Had I seen it [anti-Semitism], of course, I would have challenged it straight away.’

That might have dampened the scandal were it not for the fact that a number of other Facebook-related scandals involving him suddenly emerged.

One revolved around the revelation that he had, in 2012, used the social network to criticise a decision to remove a Nazi propaganda-style mural — depicting vile caricatures of Jewish bankers with bundles of money playing a board game resting on the backs of naked workers — from a wall in London’s Tower Hamlets.

When asked about the episode, Corbyn’s office initially claimed he’d been defending the anti-Semitic mural on free speech grounds. This position then changed with his office claiming he hadn’t actually seen the anti-Semitic mural.

‘I sincerely regret that I did not look more closely at the image,’ Corbyn said.

Newspapers then uncovered three other Facebook groups, all of which still count Corbyn as a member, in which anti-Semitic material has been shared.

One, called The History Of Palestine, carried a fake news article headlined ‘Jewish organ trafficking centre where kidnapped Syrians are stripped of their entire bodies’. The other two contained everything from Holocaust denial to Rothschild conspiracies.

And so it continues.

As to where the scandal now leads, Labour would dearly like to put the row behind it. But that seems a huge challenge.

Last night, Corbyn’s senior Labour aide son Seb was still listed as a Facebook ‘friend’ of Elleanne Green, who is supposedly suspended from the party. (Meanwhile, his youngest son, Tommy, was revealed by the Mail yesterday as having endorsed a series of vile anti-Semitic Facebook sites.)

In cyberspace, our mistakes, of course, tend to live on for ever.

So only a fool would bet against this being the last time Jeremy Corbyn’s old dalliances with anti-Semites and other extremists comes back to haunt him.