Jeremy Corbyn is launching a desperate bid to resolve the bitter antisemitism row that has wiped out six weeks of summer campaigning by his party.
At a crucial meeting of Labour's ruling body, the national executive committee (NEC), the Labour leader is hoping to reach a deal on a definition of antisemitism.
Protesters on both sides gathered for a heated demonstration outside Labour's headquarters ahead of the vote.
A group draped in Israeli flags held a sign that read: "Corbyn/Milne [his head of communications]... off our lawn! What offends Jews is our business - not yours!"
Elsewhere, people were seen holding Momentum banners and a placard that read "it's the Palestinians who are suffering" - with one man dressed in a witch's hat.
The executive is expected to adopt an internationally recognised definition drawn up by the International Holocaust Remembrance Alliance (IHRA).
But in a move that will dismay Jewish groups and anger many Labour MPs, the executive is also expected to include a so-called free speech clause, allowing criticism of Israel.
Jewish groups are also dismayed by the re-election to Labour's national executive of Peter Willsman, a veteran left-winger who claimed Jewish "Trump fanatics" were making up antisemitism allegations.
Met Police Commissioner Cressida Dick also announced on Tuesday that expert officers will investigate whether a leaked cache of complaints of antisemitism against Labour members constitute hate crimes.
The force's head of hate crime until 2017 Mak Chishty reviewed the files and told LBC that 45 of them were cases of antisemitism and 17 were race-hate incidents.
Even though a Labour Party investigation into her clash with Mr Corbyn was dropped last month, Dame Margaret is still bitterly at odds with the Labour leader and his allies.
And last week another veteran MP, Frank Field, resigned the Labour whip after a former chief rabbi, Lord Sacks, compared Mr Corbyn's record on antisemitism to Enoch Powell.
The IHRA's widely accepted definition provides 11 examples of antisemitism.
So far four of them have not been included in the Labour Party's code of conduct.
:: Accusing Jewish people of being more loyal to Israel than their home country
:: Claiming that Israel's existence as a state is a racist endeavour
:: Requiring higher standards of behaviour from Israel than other nations
:: Comparing contemporary Israeli policies to those of the Nazis
Labour has included denying Jewish people the right to self-determination is antisemitic in its own definition, and said it is "wrong" to "accuse Jewish citizens of being more loyal to Israel and to "apply double standards by requiring more vociferous condemnation of such actions from Jewish people or organisations than from others".
Claiming it is time to act to resolve the row, Corbyn ally and shadow foreign secretary Emily Thornberry told Sky News: "I think this has been a collective mess.
"I think it is a question of decisions that were made in the Labour Party, in the NEC, within the leadership. I think we should all put our hands up to this. We haven't handled it properly. The thing is, it's sickening what's now happening.
"The lack of trust between the Jewish community and the Labour Party is really dreadful. And we do now need to start working on it. You can lose trust in a moment.
"Criticism of Israel can be used as a cover, Zionism can be used as a cover for deep-seated for antisemitism and we need to be sensitive to that and we need to be aware of the fact that there are people in the Labour Party, and Labour supporters, whose behaviour and language is antisemitic. It is unacceptable.
"We need to make sure that we have a working definition, we have a proper code, that we can start applying properly, and these people have no place in our party, and we need to start kicking them out."
But former London mayor Kev Livingstone told Sky News: "We don't want to be in a position where somebody ends up being suspended for having made a legitimate criticism of Israel.
"So if we do accept this definition in exactly the way it's been poorly drafted, I think we've got to be absolutely clear that our disciplinary machine is absolutely clear about exactly how you interpret it."
Labour antisemitism campaigner Jonathan Hoffman called for the IHRA definition to be endorsed in full by the party's national executive, without any caveats, but said the Labour leader and his chief spin doctor could fall foul of that.
"If the Labour Party were to accept the IHRA definition in full, then Jeremy Corbyn and Seamus Milne and others would be put in great difficulty because you can point to any number of things they've said which infringe the IHRA definition of antisemitism," he told Sky News.
Some Labour MPs who are critical of Mr Corbyn's leadership fear the antisemitism row has already inflicted long-term damage on the party.
"Not only will the antisemitism row rumble on," Wes Streeting told Sky News, "[but] the damage to the Labour Party and the confidence in the Labour Party amongst Britain's Jews will be exacerbated and I think Labour will face a political crisis when we should be holding the Conservatives to account."
On the day MPs return to Westminster after their summer break, Labour is once again preoccupied by antisemitism.