The event, which took place on Tuesday night at St Saviour’s church in Pimlico, London, was organised by the Keep Talking Group, a small organisation devoted mainly to 9/11 conspiracy theories. Corbyn was the keynote speaker.

One of the organisers, Nicholas Kollerstrom – who has called the Holocaust a ‘primal myth’ that ‘never happened’ and claimed that the gas chambers were used only to ‘kill bugs’ – introduced Corbyn, calling him a ‘unique British scientist’.

Kollerstrom's book, Breaking The Spell: The Holocaust, Myth And Reality, was openly on sale in the hall.

The disgraced academic, who was stripped of his Honorary Fellowship by University College London (UCL) in 2008 after publishing an article entitled 'The Auschwitz “Gas Chamber” Illusion', was pictured signing books before the speech.

Also on stage was the Keep Talking Group’s founder, Ian Fantom, who had invited Corbyn to take part in the event. His group aims to prove that 9/11 and 7/7 were set-ups, and he has called David Cameron ‘every bit as bad as Adolf Hitler’.

Fantom appeared alongside Corbyn wearing a T-shirt saying ‘9/11 and 7/7 were staged’ on the back, and ‘non-violent extremist’ on the front – a reference to a phase used by Cameron to criticise conspiracy theorists.

In his speech, the well-known ‘9/11 Truther’ recommended a play called I.S.I.S., which promotes the idea that the World Trade Centre attacks were staged and features a character referred to as ‘Gay Jew Brad’.

He said: ‘Ten years ago, when my association turned on me – as the press has just turned on Trump and the British press is turning on Putin – I realised that you are judged not by the quality of your research but entirely on whether other people like the results.’

He then drew a parallel between his own work and that of Corbyn, saying that the scientist had ‘passed the Galileo test’ because he ‘stood up to authority’ in denying climate change.

Also for sale was a book by Kollerstrom, 69, entitled How Britain Initiated Both World Wars, and another exploring the idea that Paul McCartney died on ‘9/11 of 1966’ and was replaced by an impostor.

When the controversial T-shirt and books were brought to Corbyn's attention during questions from the audience, he said:

‘Sometimes it’s better not to [express my] views in public. But I think the stuff about 9/11 is pretty unbelievable. I know a lot of scientists who think so.

'In fact, I was invited over to America at one point, in fact to talk about climate, but there was a second agenda they had on to talk to me about 9/11, you know. There’s stuff [in the official explanation] that makes no sense to a rational mind.’
In a statement given to MailOnline after the event, Fantom said that Corbyn had been 'set up by the press in order to smear his brother', and that the 'distortion and manipulation' was coming from 'the Israel lobby'.

James Thring, a conspiracy theorist who has links with former Ku Klux Klan grand wizard David Duke and has campaigned for the release of Holocaust denier David Irving, was pictured at the event.

When he took the floor, Corbyn delivered a rambling lecture in which he argued that the notion of climate change had been fabricated by a global elite in order to enrich themselves and ‘control the world’.

‘This is the agenda of the globalisation story backed by the climate change authorities,’ he said. ‘You see, the climate change, it’s an ideology used to promote globalisation and the super-profits of Wall Street.’

In response to a round of applause, he smiled and made the ‘peace’ sign with his fingers, a gesture that he repeated a number of times during the event.
He added: ‘Any scare story will be used by someone to make money, whether it’s true or not. The CO2 one is false, and it’s been used to make a lot of money.

‘Kids have been brainwashed, that’s for sure.’