Video report by ITV News political correspondent Paul Brand
Jeremy Corbyn has written to Jewish critics apologising for the "pain and hurt" caused by instances of anti-Semitism in his party, as a crowd of hundreds gathered outside parliament to protest over the issue.
It is another apology from the Labour leader, who has found himself under fire from Jewish community leaders accusing him of "again and again" siding with anti-Semites.
At the protest, Jonathan Goldstein, chairman of the Jewish Leadership Council, which is one of the organisations to criticise Mr Corbyn,called anti-Semitism "a scourge on our society" that "must be rooted out".
"So we are here to say to Jeremy Corbyn: 'Enough is enough'. The time for talking is over, the time for words is over, and the time for action has begun," he told the assembled crowd, which included several MPs, among them Stella Creasy, Liz Kendall and John Woodcock.
Earlier Mr Corbyn wrote to the Jewish Leadership Council and the Board of Deputies, acknowledged that anti-Semitic attitudes "have surfaced more often" in Labour ranks in recent years.
But he said action had been taken within the party and vowed to continue a "zero tolerance" approach.
"I recognise that antisemitism has surfaced within the Labour Party, and has too often been dismissed as simply a matter of a few bad apples," he said in his letter.
"This has caused pain and hurt to Jewish members of our party and to the wider Jewish community in Britain. I am sincerely sorry for the pain which has been caused, and pledge to redouble my efforts to bring this anxiety to an end."
He also noted that criticism of Israel in relation to the "continuing dispossession of the Palestinian people" cannot be avoided.
Mr Corbyn letter was a response to an open letter by the two Jewish community groups in which they accused the Labour leader of being "ideologically fixed within a far-left worldview that is instinctively hostile to mainstream Jewish communities".
In their letter, the two groups said Mr Corbyn had been "repeatedly found alongside people with blatantly anti-Semitic views", and yet claimed to be unaware of their beliefs.
The protest outside parliament was organised by the Board of Deputies, but Jewish supporters of Mr Corbyn turned out for a counter-rally in the same place at the same time, swelling the numbers.
It was timed to coincide with a meeting of the Parliamentary Labour Party, at which MPs voiced their concerns about anti-Semitism in the party although Mr Corbyn did not attend.
The issue continues to divide the party. Wes Streeting, a Labour MP who attended the protest outside parliament, told ITV News political correspondent Paul Brand that Mr Corbyn's letter of apology was "the same old rhetoric, but light on practical action".
The Labour anti-Semitism row is longstanding, but surfaced again last week after a 2012 Facebook comment Mr Corbyn made emerged in which he offered a show of support for Mear One, the painter of an alleged anti-Semitic mural that was about to be painted over.
Mr Corbyn later said he sincerely regretted not looking properly at the "deeply disturbing and anti-Semitic" image, a sentiment he echoed in his letter, saying he was sorry "for not having studied the content of the mural more closely" before questioning its removal.
On Friday, Labour MP Luciana Berger posted a picture of Mear One's 2012 Facebook post and Mr Corbyn's comment:
The row over the mural made up only a small part of the British Jewish leaders' complaint, however.
"Hezbollah commits terrorist atrocities against Jews, but Corbyn calls them his friends and attends pro-Hezbollah rallies in London. Exactly the same goes for Hamas," the letter said.
"Again and again, Jeremy Corbyn has sided with anti-Semites rather than Jews. At best, this derives from the far left's obsessive hatred of Zionism, Zionists and Israel.
"At worst, it suggests a conspiratorial worldview in which mainstream Jewish communities are believed to be a hostile entity, a class enemy. "
In his response Mr Corbyn said such a worldview had been "long ago, and rightly, described as 'the socialism of fools'", and insisted Labour had a long history of fighting prejudice and fascism "alongside generations of Jewish men and women".
Other Jewish group's rushed to Mr Corbyn's defence.
The Jewish Voice For Labour group said they were "appalled by the actions and statements of the Board of Deputies.
"They do not represent us or the great majority of Jews in the party who share Jeremy Corbyn's vision for social justice and fairness...
"The Board of Deputies and the JLC and those supporting them must be aware that this is an attempt to influence local elections and has nothing to do with the real and necessary task of challenging racism and anti-Semitism at all levels of political life.
"We call on them to stop playing party politics and start representing what our community needs.
"We believe that is best represented by the politics we fight for and hope to see win on May 3."