Actor Hugh Grant has told the JC that Labour's leadership has not done "anything like nearly enough" to root out the "antisemitic element" within the party.
Speaking out after joining Finchley and Golders Green Liberal Democrat candidate Luciana Berger on the campaign trail on Sunday, he also said he "very much doubted" he would shake hands with Boris Johnson.
The Love Actually star, 59, was visiting the north London seat as part of his campaign to encourage "tactical voting" where pro-Remain candidates stand a chance of victory in next week's general election.
Speaking to the JC after addressing Lib Dem activists at Woodhouse Sixth Form College in Finchley, Mr Grant spoke of his admiration for Ms Berger's decision to quit Jeremy Corbyn's party.
Asked to comment on Chief Rabbi Ephraim Mirvis's intervention last week, he said: "If you ask do I think there is an antisemitic element within the Labour Party – the answer is 'yes'.
"If you ask me do I think the present Labour leadership has done anything like near enough to root it out, my answer is 'no'."
The film legend revealed he had got to know Ms Berger, whom a JC poll placed five points behind Tory candidate Mike Freer last Friday, through his work with the Hacked Off organisation.
"I knew she was a rare thing – a politician of principle," he said. "To give up the majority she had and come and fight a marginal takes a lot of guts.
"And also to face the flack of the Labour Party - these people should be cherished. They are rare in the political world."
He also said he recognised that the Finchley and Golders Green seat was "an example of where tactical voting can save the country."
"We face Brexit of the hardest kind," he said. "I don't think any sane person thinks there will be time if the Conservatives got in to make a new deal with the EU before the time period runs out.
"We are facing no deal in one year which is utterly catastrophic for this country."
Asked if he felt he would be able to shake Mr Johnson's hand, Mr Grant said: "I very much doubt he would. I don't believe I feel I have to."
He also discussed his decision not to shake hands with Chancellor Sajid Javid in October.
"I couldn't have refused to shake anyone's hand in a more charming way. I did say, 'I'm awfully sorry but I won't be comfortable doing that'."
Bemoaning the failure of the "right wing press" to hold the government to account so far in the election campaign, Mr Grant added he did not believe the BBC "has had a great election."
He added: "I am a massive fan of the BBC but something is badly amok. The fact Boris has managed to avoid a grilling from Andrew Neil is a terrible blot on the BBC's copy book.
"Having said that, there are people who say, 'well, Andrew Neill really is in a place to fully hold Boris to account.
"To be fair to him, I think he might be professional enough to do that."
Mr Grant said he was frustrated that our political system could soon allow for the UK to exit Europe with the "hardest Brexit" despite his belief that the majority in the country now wishes to remain in the EU.
"It sounds dramatic, but I don't think it is," he added. "We now have eleven days to save the UK."
Mr Grant joined Ms Berger on the doorsteps of the north London marginal meeting locals and listening to their concerns.