Scotland Yard is deploying more than 1,000 officers on the streets for a pro-Palestinian rally being held in London on Saturday.
The Met said it is expected thousands of people to travel into central London for the “March for Palestine” demonstration.
It comes amid rising tensions following last weekend’s barborous attack on Israel by Hamas militants that has claimed more than 1,300 lives.
Israel’s ensuring bombardment of the Gaza Strip - the enclave from where Hamas launched the shocking and unexpected raids - has killed more than 1,500 people and raised warnings from the United Nations and international charities of an humanitarian disaster.
In a statement on Friday, the Met said: “We are expecting thousands of people to travel to central London tomorrow to make their voices heard in a March for Palestine.
“More than 1,000 officers will be on duty to police the march, in addition to officers across the capital, and will work alongside stewards and organisers.”
Protesters have been warned flying a flag in support of Hamas is an offence which will lead to an arrest.
Deputy Assistant Commissioner Laurence Taylor, who is responsible for policing in London this weekend, said: “Our role as an independent and impartial service is to balance the right to lawful protest with potential disruption to Londoners.
“People do not have the right to incite violence or hatred. The law is clear that support for proscribed organisations is illegal.
“Anyone with a flag in support of Hamas or any other proscribed terrorist organisation will be arrested.
“We will not tolerate the celebration of terrorism or death, or tolerate anyone inciting violence.”
The police pointed out that expressing support for the Palestinian people more broadly, including flying the Palestinian flag, does not in itself constitute a criminal offence.
But a spokesperson said there were situations where a flag or banner, or the use of specific words or phrases, could be seen as intimidation, or even constitute intending to cause harassment, alarm or distress.
The Met said it has written to the Attorney General and Crown Prosecution Service to ask for “urgent clarity and guidance on charging thresholds relating to hate crime to support our policing in coming days”.
The Met said London has seen a “massive increase” in antisemitic incidents since the latest Israel-Hamas conflict erupted, from the playing of German military music to intimidation outside synagogues, the Metropolitan Police said.
Between September 30 and October 13 there were 105 antisemitic incidents and 75 antisemitic offences in the capital, compared with 14 incidents and 12 offences in the same period last year, according to figures from Scotland Yard.
The Met warned that “there is no place in London for hate.”
DAC Taylor added: “That is a massive increase in antisemitic crime and incidents.
“In balance, we have seen an increase in Islamophobic incidents, but nothing like the scale of the increase in antisemitism.
“The context is really challenging for us, we are seeing behaviours that are provocative, that are inciteful, we’ll address those whilst recognising the emotion and the activities and the incidents that are taking place overseas.”
He continued: “This will range from everything, to intimidation outside of synagogues, we’ve had incidents of German military music being played loudly and in intimidatory ways, to some more serious offences, a range of offending.
“It really is everything from that real, basic antisemitic language to some thoroughly offensive behaviour that we saw on Monday evening, where Jewish individuals were confronted by members of a protest group, effectively playing up the issues in Israel and laughing about the number of deaths of Jewish citizens in Israel.”
Officers have visited more than 200 schools as well as more than 300 synagogues, mosques and other places of worship to reassure Londoners.
The Met also has 1,000 officers dedicated to “reassurance and security patrols” in the wake of “significant concern” among Londoners which the force anticipates will continue for a “fairly long period of time”.
It also planned to have visited every synagogue in the city by the end of Friday, and has met 2,000 parents as well as pupils and schools’ leaders, amid worries about the safety of young people.