Sir Keir Starmer was met with groans as he attempted to defend Labour's position over Israel at a general election hustings for the Jewish community in the UK on Sunday, 14 May.
The shadow Brexit secretary was forced to deny that a Labour government would boycott the Middle Eastern nation after Conservative Secretary of State Sajid Javid raised Jeremy Corbyn's past support for the Boycotts, Divestment and Sanctions (BDS) initiative against Israel.
"This deserves a maturer response," Starmer said, as he addressed the Board of Deputies of British Jews in central London.
"Labour Party policy is against boycotts – I'm against boycotts. This business of saying that Jeremy may have said this, that or the other is not the way to conduct political debate.
"The Labour Party adopts policy as a party and we have a party policy on this and it's absolutely clear. We don't help by engaging in this juvenile throwing of phrases around."
The comments came just two days before the publication of Labour's general election manifesto on Tuesday 16 May. A leaked draft copy of the document stated that the party was committed to a "comprehensive peace in the Middle East based on a two-state solution".
"That means a secure Israel alongside a secure and viable state of Palestine," the policy paper added. "The expansion of Israeli settlements on the Palestinian West Bank is not only wrong and illegal, but represents a threat to the very viability of the hopes of securing a successful outcome of the peace process.
"We cannot accept the continued humanitarian crisis in the Occupied Palestinian Territories, and we will support Palestinian recognition at the UN."
Elsewhere, the issue of anti-Semitism was raised during the debate between Starmer, Javid, Liberal Democrat peer Baroness Ludford and the SNP's Kirsten Oswald.
Javid described Labour's internal anti-Semitism inquiry, led by now Shadow Attorney General Baroness Chakrabarti, as a "whitewash".
Starmer, meanwhile, said that former Mayor of London and Corbyn ally Ken Livingstone should have been expelled from the party rather than be suspended for claiming that Nazi leader Adolf Hitler supported Zionism in the 1930s. "I said he should have been expelled because zero-tolerance means zero-tolerance," he said.
Starmer added: "The Labour Party has fought anti-Semitism for years. It pains me for the last two years [there has been an] association or even a discussion about my party and anti-Semitism."
But despite the Labour spokesman's spirited defence of his party, a 2016 poll from Survation for the Jewish Chronicle found that just 8.5% of British Jews would vote for Labour at a general election.