A Labour Election candidate organised and ran a secret Facebook group which advises party members, including alleged Holocaust deniers, how to beat charges of antisemitism.

Maria Carroll, a Jeremy Corbyn ally who is standing in the marginal seat of Camarthen East in Wales, co-founded and administered the site which instructed Labour Party members accused of antisemitism on how to avoid expulsion.

Among those who joined the group are members who cast doubt on the murder of six million Jews by the Nazis and others who repeated the antisemitic trope that there is an international ‘Jewish conspiracy’ controlling politics, the economy and the media.

The Mail on Sunday has established that Carroll personally advised alleged Holocaust deniers. Yesterday she said she had not seen the social media posts in which they circulated these repellent views.

One of those advised by the secretive organisation last year was Peterborough Council Labour candidate Alan Bull.

Maria Carroll (pictured), who is standing in the marginal seat of Camarthen East in Wales, co-founded and administered the site which instructed Labour Party members accused of antisemitism on how to avoid expulsion

In June 2015, salsa teacher Bull posted a link on Facebook to a website that claimed ‘the murder of six million Jews is a hoax’. He also shared posts which claimed Tony Blair’s New Labour had been a ‘Mossad front’, and that Mossad, the Israeli intelligence agency, murdered Diana, Princess of Wales. He was selected as a council candidate in October 2017.

At first Bull claimed his posts had been ‘doctored’, but later admitted they were ‘a bad mistake’. He did not respond to requests for comment.

Labour’s official watchdog, the Compliance Unit, investigated Bull after receiving two complaints.

While he was under investigation, the secret Facebook group, which calls itself the ‘Labour Party Compliance: Suspensions, Expulsions, Rejections Co-Op’, advised him how to defend himself.

Administering the group with Carroll was Caroline Tipler, a reiki therapist, who told Bull he should file a subject access request with the party using the Data Protection Act – which would mean getting access to any information the party held on him.

She advised him not to co-operate with the unit until this request was met. She boasted that this approach worked: ‘Since we have been challenging their process over and over again, they are now backing off.’

Carroll urged Bull to delete all social media posts about his case other than those in the secret group. He was eventually forced to stand down as a candidate.

Tipler told Bull the posts he had shown her were ‘anti-Zionist but not antisemitic’. Last night, Tipler said she had blocked him from the group when she discovered he had denied the Holocaust.

Another member of the secret group who allegedly denied the Holocaust is Mollie Collins, a retired media researcher from Weymouth. She stood as a Labour county council candidate and until July this year was chairman of Dorset Labour. In January 2016, she posted a link on Facebook to a website claiming: ‘How the Holocaust was faked’. In Facebook posts from 2015, she shared claims that the Rothschilds, the Jewish banking family, ‘took down’ the missing Malaysian MH370 airliner, and that the BBC was ‘a mouthpiece for Israel’.

Collins was given instructions by the group on how to complain about the way an investigation by the unit had been handled. Yesterday Collins claimed her posts were fabricated by people opposed to a Jeremy Corbyn government, using ‘military grade artificial intelligence’. She recently resigned from the Labour Party.

Carroll also gave advice to Exeter Labour activist Sue Grant. In 2014 Ms Grant shared a Facebook post saying Israeli Jews were as bad as the Nazis, and in January 2016 she posted that she was sharing a link to a film which claimed the Nazi extermination camps were ‘not DEATH CAMPS!!!!’

The Facebook group does not show up in internet searches and its membership list and postings are invisible to non-members.

But this newspaper – working with campaign group Labour Against Antisemitism and Gnasherjew, a group of investigators who left Labour over its antisemitism – has seen hundreds of posts, and a list of more than 400 members. It includes councillors, candidates and party officials.

In one group post, Carroll warned that if its existence were exposed, it would be damaging. She posted: ‘REMINDER: Posts from this group are not to be shared. Comments are not to be screenshot.’

Last night Carroll said she had not seen posts in which Bull and Grant appeared to deny the Holocaust, saying if she had ‘I would have immediately condemned them’. She said she was ‘an outspoken critic of antisemitism in our party’.

She said she joined the secret group when ‘Left-wing members were being suspended from the Labour Party to prevent them from voting in the 2016 Labour leadership election… When a small number in the group took an antisemitic conspiratorial direction I left it.’ Her most recent post to the group was in May this year.

Last night MP Margaret Hodge, said: ‘I have been raising concerns about Jew-haters not being booted out of the party for a long time. I will be writing to the leadership demanding an immediate inquiry.’

Denny Taylor, spokesman for Labour Against Antisemitism, said: ‘This confirms that the Labour Party has spent the last four years encouraging a toxic culture of anti-Jewish discrimination to flourish. Responsibility must be levelled directly at Mr Corbyn.’