A former aide to Jeremy Corbyn reportedly told the Sunday Times that he informed Shami Chakrabarti of his concerns about anti-Israel rhetoric within the office, but that these were not included in her report into anti-Semitism.

According to the article, Josh Simons, a former policy advisor who is Jewish, is alleged to have told Chakrabarti that someone referred to a “Jewish conspiracy” in the office.

It is not clear who made the alleged comments, or when, but it is believed to have been made in response to Ken Livingstone being approached by John Mann MP, the chairman of the All-Party Parliamentary Committee on Anti-Semitism, in light of the former mayor’s comments that “Hitler was a Zionist”.

The Sunday Times reports the “friend” of Simons as saying he told Chakrabarti that Corbyn’s chief of strategy Seamus Milne had “at best a blind spot with anti-Semitism and at worst a wilful disregard for it”.

Chakrabarti, who has been offered a peerage by the Labour Party, said her remit was not to investigate individual instances and allegations but to come up with recommendations and guidelines for future conduct.

However, the “friend” said Simons was left angry when she was named as Labour’s nominee for the House of Lords, saying: “When Josh read the report he was bitterly disappointed, he thought it was a whitewash, but when Shami’s peerage was confirmed he was angry – he thinks it was a classic stitch-up.”

Corbyn’s office dismissed the reports as “false and part of the campaign against his leadership”. A spokesman added: “The person making these claims is a disgruntled former member of staff.”