Under-fire Labour general secretary Jennie Formby twice told a meeting of MPs and peers that it was impossible to fully "eradicate" antisemitism from her party, the JC can reveal.
Attempting to convince Monday's meeting of the Parliamentary Labour Party (PLP) that under Jeremy Corbyn's leadership there was a concerted effort to tackle Jew-hate, she said: "I don't think anyone can ever say that we can eradicate antisemitism completely and stop every single person from making ... every single day someone else could join the party tomorrow and do something.
"What I want to make sure is that we have processes and procedures that deal with people who do (engage in) antisemitism within our party.
"And I think that's very important."
She then added: "Anyone who thinks that they can completely eradicate something - then they are being dishonest."
After Ms Formby made her controversial remarks - in front of a packed meeting that was observed in silence by shadow Home Secretary Diane Abbott, shadow chancellor John McDonnell and party chairman Ian Lavery - angry backbench MPs openly voiced their anger.
Resentment increased after Ms Formby confirmed she would not be able to provide a full report answering all eleven questions relating to Labour's disciplinary processes over antisemitism.
The successful motion, which had been proposed by Newcastle North MP Catherine McKinnell, demanded answers from the leadership in one week. It was unanimously passed by the PLP at the packed meeting in Westminster.
Ms McKinnell queried whether there really was a "commitment for this report to come before the PLP next Monday."
And Dame Margaret Hodge protested to John Cryer, who chaired the meeting: "Jenny has just told us she is not going to comply with the terms of the resolution that has been passed unanimously by this PLP. In those circumstances what are you going to do and what are other members the NEC going to do protect our rights to have that information?
"I've never heard such a vacuous argument, if one really does want to kill that terrible cancer of people feeling we've become institutionally antisemitic.
"The most important thing you can do is provide the information and data."
Ilford North MP Wes Streeting also complained about the lack of "transparency" from the leadership over the backlog of outstanding antisemitism cases.
He said: "Frankly in terms of the data we demand off government when it comes to the types of cases, the numbers of cases, and how they are dealt with - we expect transparency from government - is it not unreasonable to expect it from the party?"
Mr Streeting then made reference to the need for "public transparency", which he said "is the only thing that will help to resolve this."
He added: "Me going back to my constituents saying, 'Don't worry Margaret, George and Shabana (three members of the party's NEC) are on the case’ will honestly just not cut it."
Dame Margaret added: "I'm confused, We have just passed this motion unanimously. We therefore expect all the information before us next week. "
Luciana Berger them told the meeting that the report circulated by Jennie Formby ahead of Monday's meeting "doesn't answer" the questions raised in the PLP motion.
In a further revealing admission, Ms Formby told the meeting - attended by other senior figures such as Harriet Harman and Yvette Cooper - that she had attempted to engage with Jewish communal groups and organisations since Labour adopted the IHRA definition of antisemtism last September.
She confessed that nobody should "under estimate the anger and stress community groups and particular individuals feel about this."
She added that "at the present time" communal groups "haven't felt that it's appropriate to engage with us in such a way."
But she then added: "I have spoken with individuals who are in the organisations - and I'm not talking about people who are in fringe groups. I have done so on a very confidential basis because I am attempting to find a way to get guidance on how we do the difficult things, we change our procedures, deal with the difficult issues. Rebuilding trust is something that is much more important."
On Monday night, Labour sources aimed to calm the anger over Ms Formby's remarks suggesting she was saying you cannot eradicate antisemitism without education and good procedures.
A Labour source added: "Jennie Formby gave a comprehensive update on the significant work that's been done to strengthen and speed up procedures and addressed the points of the motion.
"Complaints processes are confidential and the party has a responsibility to protect members data."