The Equalities and Human Rights Commission (EHRC) has written to the Labour whistleblowers who gave evidence of antisemitism in the party, saying it may use this to question the leadership over Jew-hate.
It also said that they “may also refer to information provided” in its final report, once they have completed its investigation.
In the letter – originally published by Sunday Times journalist Gabriel Pogrund and dated January 6 – EHRC Senior Principal Stephen Lodge said: “We have identified a need to use some of the information you have shared with us for the purposes of our investigation.
“We intend to use the information you have provided as a basis for certain questions to the Party on areas within the Terms of Reference, for example where it relates to the sample of complaint files under investigation and how these were handled, or the general investigatory and disciplinary processes used to handle complaints.”
The Labour is only the second UK party to be investigated by the EHRC, after the far-right British National Party.
Last month, the Jewish Labour Movement submitted a 53-page dossier to the EHRC investigation which said Labour suffered from the "corrosive disease" of institutional racism through "unwitting prejudice, ignorance, thoughtlessness and racist stereotyping."