© TLA NewscomJeremy Corbyn speaking against the 2009 Israeli bombing of Gaza. An estimated 50,000 people demonstrated in London.
Left-wing group Jewish Voice for Labour has praised Corbyn's "consistent commitment to anti-racism" and condemned current right-wing attacks.
The show of support comes after two Israel lobby groups issued a call on Sunday to demonstrate against alleged anti-Semitism in the Labour Party, for which they hold Corbyn responsible.
But Jewish Voice for Labour has called an emergency rally as a counter-demonstration, accusing the Board of Deputies of British Jews and the Jewish Leadership Council of "playing party politics" ahead of May's local elections.
Mick Davis, chief executive of the ruling Conservative Party, is former chairman of the Jewish Leadership Council - a leading part of the UK's Israel lobby.
On Monday morning's edition of BBC Radio 4's flagship Today program, the Jewish Leadership Council's current chairperson Jonathan Goldstein issued an unprecedented personal attack on Corbyn.
Goldstein claimed that "Jeremy Corbyn is now the figurehead for an anti-Semitic political culture, based upon obsessive hatred of Israel, conspiracy theories and fake news."
Labour Witch Hunt
Since Corbyn became leader of the Labour Party in 2015, he has faced relentless attacks from right-wingers and supporters of Israel due to his long-standing support for Palestinian human rights.
Exaggerated and often entirely fabricated charges of anti-Semitism against Labour activists have been used to attack Corbyn and his grassroots supporters.
These activists have often been Jewish themselves, targeted for supporting Corbyn and for longstanding Palestine solidarity activism.
Polls ahead of May's local elections have predicted that Labour under Corbyn will make significant electoral gains.
Jewish Voice for Labour on Monday accused the Israel lobby and its allies of using the current wave of anti-Semitism allegations to undermine Labour's chances.
Appalling
The JVL statement said that as Jews in Labour currently campaigning in local elections, "we are 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."
"Jeremy's consistent commitment to anti-racism is all the more needed now," the group added.
Jewish Voice for Labour also accused Israel lobby groups of being "silent" on the "massively more anti-Semitism on the right of politics."
They pointed to a "senior ex-adviser to the prime minister who recently used a national newspaper to dredge up anti-Semitic conspiracy theories."
In February former Theresa May advisor Nick Timothy wrote an article in the Conservative-supporting Telegraph accusing Jewish billionaire George Soros of a "secret plot to thwart Brexit."
The piece was widely condemned for "dog-whistle anti-Semitism."
But some on the pro-Israel right supported the piece. Anti-Muslim journalist Melanie Phillips claimed "there was nothing whatsoever anti-Jewish, with or without the dog-whistle, in anything Timothy wrote."
Soros is often a hate figure for right-wing anti-Semitic conspiracy theorists, especially those promoted by the Hungarian government - which is closely allied with Israel.
Mark Elf, the Jewish anti-Zionist who has for years blogged at Jews Sans Frontieres tweeted on Monday evening that the Jewish Voice for Labour counter-demonstration outnumbered the pro-Israel one.
Times correspondent Lucy Fisher tweeted that there were ten Conservative lawmakers at the demonstration, but only a "handful" of Labour lawmakers "milling around solo."
Mural Controversy
The current wave of right-wing, anti-Palestinian attacks on Corbyn's leadership was triggered last week after a Facebook comment by Corbyn from six years ago was dredged up.
Labour lawmaker Luciana Berger Tweeted a screenshot of Corbyn commenting on Facebook in 2012, criticizing the removal of a mural in East London titled "Freedom for Humanity."
Berger is parliamentary chairperson of the Jewish Labour Movement - a group which lobbies for Israel and has strong links with the Israeli embassy.
The group said in a statement on Sunday night it would be joining the demonstration against Corbyn.
Corbyn responded to Berger with regret over the old Facebook comment and said he should have "looked more closely at the image" of the mural first.
He also issued a statement on Sunday saying he was "sincerely sorry for the pain which has been caused" by what he described as the "anti-Semitism [which] has occurred in pockets within the Labour Party."
Conspiracy theories
Mear One, the Los Angeles artist behind the 2012 mural, on Sunday denied it was anti-Semitic.
In a 2012 video showing how he painted it, he said it depicted "the elite banker cartel known as the Rothschilds, Rockerfellers, Morgans, the ruling class elite few, the Wizards of Oz ... The symbol of the Free Mason pyramid rises behind this group."
Lutfur Rahman, a left-winger and then the elected mayor of Tower Hamlets in East London, had the mural removed, saying at the time that whether "intentional or otherwise, the images of the bankers perpetuate anti-Semitic propaganda about conspiratorial Jewish domination of financial and political institutions."
In the late 19th century, some leading members of the Rothschild banking family financially supported early Zionist colonization of Palestine.
Indeed, the infamous Balfour Declaration - which announced the British Empire's intent to hand Palestine over to colonization by the Zionist movement - was addressed to Lionel Walter Rothschild.
Zionism, however, was an idea intricately tied to British imperialism and principally supported by Christian Zionists, while being opposed by a majority of prominent British Jews at the time.
Yet British and American anti-Jewish and right-wing conspiracy theorists ignore these facts and regularly cite the Rothschilds' role in Palestine as part of their claims asserting secretive "Rothschild" control over the world.
Palestinians have repeatedly made clear that they want such conspiracy theorists to have no part in their struggle.
Updated since publication.
Comment: Corbyn's growing power as a reasonable, articulate voice for non-imperialism must be stopped at all costs. However desperate, smearing Corbyn with the 'anti-semitic' label is merely another emotionally charged tool being used to delegitimize him and all he stands for.