But following the letter’s publication on Sunday, which said Mr Corbyn has “bent over backwards to help Jewish people” the JC has established four signatories were not shown its full text in advance.
At least one of those who named as a signatory signed after being told only that the letter that would affect “the very future of the Jewish people in this country”.
Another signatory Hyman Bindinger, 81, from Tyne and Wear later said he had been approached at a wedding and asked for his signature on a letter he did “not understand.”
Mr Bindinger added: “I made a mistake. He showed me that other people signed and I thought ‘I will sign it’… I do not understand what it’s about. I hardly know who Corbyn is.”
Among those who signed the letter was Hungarian-born Avigdor Langberg, who later founded Kay’s Supermarket and Deli on Golders Green Road.
But when the JC spoke with a member of Mr Langberg’s family, they said the issue was a “very painful one” to discuss and insisted they would not want the family business to be associated with being supportive of Mr Corbyn.
Another of the signatories spoke with a leading figure in the Stamford Hill Charedi community on Monday in distress, having learned about the wording of the letter after it was published.
The signatory said they had been asked to sign the letter by a known associate of Mr Stern, who has become closely linked with Mr Corbyn over recent months, and again told that their signature was required a letter protecting the” very future of the Jewish people.”
Sources have also told the JC that at least two of the signatories on the letter are particularly elderly and unlikely to have been able to read the text they had signed in full.
The JC can also reveal that the Sunday Times cut a paragraph from the letter that said “in terms of Holocaust history” the Board of Deputies “frustrated and hindered rescue efforts” during the Second World War.
The paper edited this from the published version of the letter, apparently amid concern about the strength of the claim.
The JC has approached Mr Stern for comment.
Geoffrey Alderman, who works as an advisor for Mr Stern, told the JC: "I played no part in the collection of signatures.”
Earlier this week, Mr Stern sparked anger after sending an email on Saturday evening to “Dear Kapo Pinter” - addressing Rabbi Avraham Pinter, chairman of the Union of Orthodox Hebrew Congregation's (UOHC) external affairs committee.
The pair have disagreed repeatedly over recent months over the community's responses to changes to government education policy
“Kapo” was a term for prisoner in a Nazi concentration camp who was assigned by the SS guards to supervise forced labour.
"Why are the Christians not aware of your deal with the DfE? I just need that reassurance once more," Mr Stern wrote in his email, which urged people to lobby their MPs to vote against draft regulations on relationships and sex education.
"Never argue with a liar. You can't win because they believe their own lies."
Mr Stern’s email immediately sparked outrage among many in the Stamford Hill community. One senior Jewish communal figure revealed to the JC they had sent Mr Stern an angry email.
