Jewish Labour MP Dame Margaret Hodge has expressed fresh concerns about how her party is handling accusations of anti-Semitism.
In a letter to Jeremy Corbyn, she claims she has been misled over assurances that his office was not involved in any disciplinary process.
"Either you have intentionally misled me or your staff have been misleading you," she complained.
Labour has dismissed her suggestion as "categorically untrue".
Dame Margaret's letter refers to a report by the Observer claiming that internal documents showed senior Labour figures last year opposed recommendations to suspend several party activists accused of anti-Semitism.
The Barking MP wrote that she had been left "bewildered" by the account in the newspaper which "contradicts what you told me to my face last week".
Last week Corbyn reassured me categorically that his office never intervened in antisemitism complaints. @ObserverUK whistleblower account clearly shows Corbyn’s office have intervened. Either Corbyn has intentionally misled me or his staff have misled him. Full letter below pic.twitter.com/gUR6LvJ3QW— Margaret Hodge (@margarethodge) March 5, 2019
Referring to a discussion she had with Mr Corbyn, she said: "I distinctly remember it being said that it would be appalling if staff in the Leader's Office intervened or had a role in complaints.
"I was given categorical assurances that this does not happen and has never happened.
"However, it is clear from the whistleblower's account [in the Observer] that your staff did intervene and have had a direct role in complaints."
Dame Margaret also says she is disappointed that Labour peer Lord Falconer is being considered to lead an investigation into anti-Semitism in the party.
Dame Margaret told BBC Radio 4's Today that Mr Corbyn had given her "absolute, copper-bottomed undertakings that there was no interference in the complaints process by his inner circle, by his top team".
However, she claimed "a whole number of his top team, not just one person, lots of them" were involved in decisions about individual complaints, adding: "They interfere and they lower the sanctions. People aren't suspended, they're just given a warning letter.
"What is so awful about this is that Jeremy always proclaims zero tolerance of anti-Semitism. When it comes to the actual cases, if they're his mates he doesn't demonstrate zero tolerance."
She added she had seen "so much evidence" of political interference, adding: "Trust in him is gone."
Dame Margaret also questioned whether Lord Falconer was the appropriate person to conduct an inquiry into the party's handling of anti-Semitism allegations.
The former Lord Chancellor is considering whether to take on the role and wants reassurances from the party that he will be given the resources he says he needs.
He has said he wants to examine claims Labour is institutionally anti-Semitic and how to restore faith in the party's disciplinary procedures.
He told BBC Radio 5's Pienaar's Politics many Labour members believed the treatment of cases depended on "who your friends are".
But Dame Margaret said she did not think Lord Falconer was independent enough.
She claimed his inquiry could be a repeat of the one carried out by Labour peer Baroness Chakrabarti in 2016, which found that the party was 'not overrun by anti-Semitism'.
"We need somebody totally outside the Labour Party otherwise this becomes another Chakrabarti fiasco," said Dame Margaret.
She claimed Lord Falconer had "bombarded" her with phone calls last summer, when she was facing disciplinary action - later dropped - over an angry confrontation with Mr Corbyn, to try to "force me to give an apology".
In response, Lord Falconer said: "I am shocked she thought I was trying to pressurise her into apologising for calling Jeremy Corbyn and anti-Semite. I was just trying to urge the party to drop their complaint against her."
He told BBC Politics Live presenter Jo Coburn he would be independent of the leadership and investigate any complaints of anti-Semitism in the strongest possible way, but he had not yet accepted the job.
Responding to @margarethodge questioning his independence as Labour’s new surveillance commissioner @LordCFalconer told me he’d be independent of the leadership and investigate any complaints of antisemitism in the strongest possible way. He has yet to formally accept the role.— Jo Coburn (@Jo_Coburn) March 5, 2019
A Labour Party spokesman said: "Any suggestion that staff in the Leaders' Office overturned recommendations on individual cases is categorically untrue."
He added: "Since becoming general secretary, Jennie Formby has made procedures for dealing with complaints about anti-Semitism more robust.
"Staff who work on disciplinary matters have always led on investigations and recommendations on individual cases."
Ms Formby - a former Unite union official - is the most senior employee of the Labour Party and is in charge of its 400 or so backroom staff.
The party's leadership has been accused of tolerating a culture of anti-Semitism by a number of MPs who have quit the party, including Luciana Berger and Joan Ryan.
Ms Berger said she had come to the "sickening conclusion" that the party had become institutionally anti-Semitic and that she was "embarrassed and ashamed" to stay.
'Loss of trust'
Mr Corbyn has insisted he is "committed to eliminating anti-Semitism wherever it exists".
"Prejudice and hatred of Jewish people has no place whatsoever in the Labour Party," he said earlier this year.
Deputy Labour leader Tom Watson has spoken of a "complete loss of trust" in the party's processes and has asked MPs to forward anti-Semitism complaints to him as well as the party.
That call prompted Ms Formby to accuse Mr Watson of "unacceptable" behaviour and claim he was trying to undermine her work.