“While you foment your campaign of allegations of antisemitism against Corbyn and the left to silence Israel's critics while you cry wolf, month after month, year after year in the Labour Party and remain blind to the explosion of the far-right and Islamophobia, you are not part of the solution - you are part of the problem.”
Mr Corbyn and his shadow chancellor John McDonnell had openly supported the march on which there were regular calls for the destruction of Israel, the “right of return” for “seven million Palestinian refugees” and claims by one speaker that Israel, America, Australia and India are “despicable settler colonial states.”
Three counter-demonstrators - two of whom raised an Israeli flag while another professed “love for both Israel and Palestinian - needed protection from around ten Metropolitan Police officers on Regent Street after a succession of visibly seething activists attempted to lunge at them.
Mr Secker, also an executive member of the Jews For Justice for Palestinians group, attempted to link “Jews” to the far-right English Defence League. He spoke of a “fifth column” inside the Labour Party - naming veteran Jewish MP Dame Margaret Hodge, deputy leader Tom Watson and the Jewish Labour Movement.
Mr Secker told the crowd - many of whom carried official Labour Party CLP banners and who regularly chanted “Israel is a terrorist state” - that “we have our own [US] Republicans here - a fifth column inside the Labour Party. 190 Labour Friends of Israel MPs led by Hodge and Watson and the Jewish Labour Movement.”
Mr Secker added: “It's not about antisemitism here either. The Labour Party's general secretary Jennie Formby has established the serious cases amount to 100th of 1 per cent.
And Jewish leaders are turning a blind eye to the extreme right even when their own Zionist federation praises the English Defence League, the neo-fascist group banned on Facebook.
“What on earth are Jews doing in the gutter?”
When confronted later by the JC over his remarks, Mr Secker claimed not to have spoken of “Jews”.
In a statement on Twitter, JVL suggested he had directed his comments towards “these Jews” - those who had allegedly aligned themselves with the far-right. The audio recording however shows no use of the word “these”.
Mr Secker - a former member of the far-left anti-Zionist Socialist Workers Party - has previously been the subject of complaints from Jewish members of his local Labour Party about his hostile comments.
He was also a member of the Palestine Live Facebook group which was littered with antisemitic remarks.
Shadow Justice Secretary Richard Burgon - who was exposed recently for saying that Zionism was the enemy of peace, remarks he had denied but which were captured on video - told the crowd: “Palestinians should be able to live free from ever expanding settlements on stolen land.”
Directly before him, Ahed Tamimi, the 18-year-old who became an icon of the Palestinian cause after she was jailed for slapping an Israeli soldier on film, received loud cheers as she called herself a freedom fighter before shouting: “From the river, to the sea, Palestine will be free.”
Husam Zomlot, the Palestinian ambassador to the UK, told the crowd to loud cheers that Ms Tamimi “is Palestine.”
But in his speech he was one of the few to make clear he recognised the right of Israel to exist - albeit under pre-1967 borders.
Ahead of Saturday's march, which ended in Whitehall, Jeremy Corbyn had expressed his support for those attending.
In a statement that failed to acknowledge more than 650 rockets had been launched by Palestinian militants into Israel ahead of last weekend's latest clashes, Mr Corbyn had said: “We cannot stand by or stay silent at the continuing denial of rights and justice to the Palestinian people.
“The Labour Party is united in condemning the ongoing human rights abuses by Israeli forces, including the shooting of hundreds of unarmed Palestinian demonstrators in Gaza - most of them refugees or families of refugees - demanding their rights.”
Shadow chancellor John McDonnell also issued a message of “support and solidarity” ahead of the march.
In a speech from the stage in Portland Place at the start of the demo - organised by the Palestine Solidarity Campaign and the Stop the War Coalition - a representative from the Key48 pro-Palestinian student movement in the UK had launched an astonishing attack on what she described as the “settler colonialist” states of Israel, America, India and Australia.
'Hannah', the speaker for the Key48 group - who argue for the “right to return” for “all Palestinian refugees” - said: “The root of the problem is settler colonialism. It is no coincidence that Israel's staunchest allies include America - another despicable settler colony still oppressing indigenous native Americans on native American soil.
“It is no coincidence that Australia, the next in line to move their embassy to Jerusalem, another despicable white supremacist settler colony still oppressing the indigenous Aboriginal people.
“And it is no coincidence that India's Prime Minister is hosting Netanyahu on frequent state visits in India's most lavish and luxury hotels and restaurant's while both are complicit in the brutal occupation of Kashmir.”
Also addressing the crowd was Karen Mullen, from Sinn Fein, who drew loud applause after she falsely accused Israel's IDF of killing a pregnant Palestinian and her 14 month niece during violence in Gaza last week.
Ms Mullen said: “What about the 14 month old baby who was murdered by Israeli military - how disgraceful is that?
“Where is the international outrage?”
Evidence that a stray missile responsible for the tragic deaths was actually fired by Islamic Jihad was ignored by Ms Mullen, who joined the RMT union's Steve Hedley in attempting to draw a direct link between the events in Gaza with the alleged actions of the British military in what was described as the “occupied six counties.”
The current chair of the Palestine Solidarity Campaign said he was “prouder to tell” the crowd “I come from Jerusalem, the capital of Palestine.”
He added: “We want Israel to exit Palestine, so the Palestinians can be free.”
