Jeremy Corbyn was called “an antisemite” to his face by veteran Jewish Labour MP Dame Margaret Hodge when she confronted him in the House of Commons.
Dame Margaret approached the Labour leader behind the Speaker's Chair once votes on Brexit were over on Tuesday evening.
Furious that the party upheld controversial new guidelines on antisemitism, in the face of huge opposition from British Jewry, she told Mr Corbyn: "You’re an antisemite and a racist.”
She added: “You have proved you don’t want people like me in the party."
Mr Corbyn is alleged to have responded: "I'm sorry you feel like that."
The confrontation was initially reported by HuffPost, which alleged she used the words "f***ing antisemite". The JC understands Dame Margaret has denied swearing.
A second source - another Labour MP - then confirmed to the JC that reports of the bust-up were "totally true."
The confrontation happened away from cameras that record parliamentary proceedings.
A party source told HuffPost: “She was aggressive, Jeremy was calm. Other MPs who were there were upset by it."
Sources say Mr Corbyn is now likely suggest a meeting with Dame Margaret to clear the air - although she is likely to be referred to Party whips for misconduct charges.
Dame Margaret is a former chair of the Public Accounts Committee, and has long criticised Mr Corbyn’s leadership.
She was one of the MPs who triggered a vote of no confidence in him in 2016, triggering a second leadership election.
The MP for Barking described earlier this year how she had joined the Labour Party in the 1960s because it was a party that stood up for minorities and against racism.
“I never ever thought I would experience significant antisemitism as a member of the Labour party,” she said.
“I have, and it has left me feeling an outsider in the party of which I’ve been a member for over 50 years… I have never felt as nervous and frightened as I feel today about being a Jew.
“It feels that my party has given permission for antisemitism to go unchallenged. Antisemitism is making me an outsider in my Labour Party.”