Paul Eisen, the self-professed Holocaust denier, has given Jeremy Corbyn his support in an extraordinary blog post in which he says that he has been close to the Labour leadership contender for more than 15 years.

'One evening 15 years ago I cycled over to see [Corbyn],' he writes. 'I was just beginning to establish Deir Yassin Remembered [a controversial, pro-Palestinian pressure group] in the UK and I wanted him to join.

'I'd hardly begun my feverishly-rehearsed pitch before his cheque book was on the table.

'From that day on, without fuss or bother, whether DYR was flavour-of-the-month or the maggot-at-the-bottom-of-the-food-chain, he attended every single Deir Yassin commemoration.'

Paul Eisen, left, is a self-professed Holocaust denier who frequently shares anti-Semitic and far-Right content on his blog. Jeremy Corbyn, right, who according to Eisen has attended 'every single' one of his organisation's annual events, appears to sit attentively during one such meeting in St John's Wood Church in 2013

The group that Eisen mentions, Deir Yassin Remembered (DYR), focuses on controversial allegations that Jewish soldiers killed about 100 Arab villagers in the run-up to the war of 1948, and seeks to promote its remembrance at annual events.

It highlights the fact that the village of Deir Yassin is situated close to Yad Vashem, Israel's Holocaust museum.

Many mainstream Palestinian activists view the group as anti-Semitic and in thrall to 'anti-Semitic conspiracy theories'.

In 2007, the Palestinian Solidarity Campaign proposed a motion disowning Eisen's group, stating that 'membership or participation in DYR is incompatible with being a member of Palestinian Solidarity Campaign. You cannot oppose racism against the Palestinians and turn a blind eye to anti-Semitism.'

The DYR website contains a picture appearing to show Corbyn attending one of the organisation's event in 2013 (above).

Politicians need not only to condemn antisemitism but be seen to distance themselves from it Jonathan Sacerdoti, Campaign Against Antisemitism Jonathan Sacerdoti, Campaign Against Antisemitism

Eisen's open Holocaust denial has made him a toxic figure among many pro-Palestinian activists.

'I question that there ever was an official plan on the part of Hitler or any other part of the National Socialist Regime systematically and physically to eliminate every Jew in Europe,' Eisen has written on his blog.

'I question that there ever existed homicidal gas-chambers… Deny the Holocaust! For my money, a child of six can see that something's not right about the Holocaust narrative... For me, "Holocaust Denier" is a label I accept.'

The alleged relationship with Eisen will be particularly embarrassing for the Labour leadership contender as the Holocaust denier believes Corbyn stood by him when he felt ostracised.

On his blog, Eisen recalls a period when he felt 'despised' by mainstream society, and only Corbyn refused to shun him.

'During the time when I felt so marginalised and isolated, when the movement with which he was associated so despised me, Jeremy always said hello,' he wrote.

Popular: Jeremy Corbyn sits on a stage surrounded by members of the Labour party in Bradford

Rhetoric: Jeremy Corbyn makes a speech in Bradford amid revelations that he has 'links' to a notorious Holocaust denier

Supported: Jeremy Corbyn arrives in Bradford to give a speech to Labour voters

Eisen is also a supporter of David Duke, the former Ku Klux Klan grand wizard, 9/11 'truther' and notorious conspiracy theorist.

When promoting a Duke video entitled The Zionist Red Army on his website, Eisen wrote: 'Oh, how I wish I could stop posting David Duke (it gets me into no end of trouble). Trouble is, he just will not stop telling the truth.'

The video in question includes an extended anti-Semitic rant by Duke. Towards the end, he says: 'The people of Europe and America, [the Jews are] coming for you… Together we will defeat the true apostles of hate'.

Eisen also promotes articles from a prominent White Supremacist website on his blog. One of these, posted in March, refers to Jews as 'rats' and talks of the 'battle we wage' against 'international Jewry'.

Jonathan Sacerdoti, Director of Communications at the Campaign Against Antisemitism, said:

'No politician should have any association whatsoever with a Holocaust denier like Paul Eisen. It is disturbing to see these pictures of a potential Leader of the Opposition at one of his events.

'Politicians need not only to condemn antisemitism but be seen to distance themselves from it.'

Eisen could not be reached for comment.

These latest revelations raise serious questions about Corbyn's association with extremists of all stripes.

The Islington MP has previously referred to Hamas and Hezbollah as his 'friends', and has invited convicted IRA members to Parliament. On Thursday, he refused five times to condemn IRA atrocities when interviewed by BBC Radio Ulster.

Jonathan Arkush, President of the Board of Deputies of British Jews, said: 'Paul Eisen is a notorious Holocaust denier and if Jeremy Corbyn does have links with him this would be very alarming. We would ask Mr Corbyn to clarify the situation.'

A spokesperson for Jeremy Corbyn's campaign said:

'Paul Eisen is not someone Jeremy Corbyn's office has any dealings with. Based upon what is in written in the articles here, anyone can call themselves a “long time associate” when in fact that is not the case. Paul Eisen clearly holds some of the most extreme views that are entirely his, and Jeremy totally opposes them and disassociates himself from them.'

When asked to confirm whether Corbyn knows Eisen personally, or whether Eisen's accounts of Corbyn attending 'every single' one of his events and 'opening his cheque book' to his organisation are correct, the spokesperson declined to comment.