The march in Marble Arch in central London followed the 7 October surprise terror attack by Hamas and the Israeli response. Protesters held signs that read “Freedom for Palestine” and “Stop bombing Gaza”.
The Metropolitan police estimated that about 100,000 people had turned out by 2pm on Saturday. The frontmost marchers moved along Park Lane, via Hyde Park Corner, Piccadilly and Trafalgar Square to reach Whitehall and, by 3pm, protesters had reached Parliament Square. By 5pm, much of the crowd had dispersed.
A total of 10 arrests were made linked to the protests in London and five police officers sustained minor injuries, the Metropolitan police said.
The arrests were for offences involving fireworks, public order and assaulting an emergency service worker.
Two people were earlier arrested after fireworks were launched at officers in Trafalgar Square, the Met said.
The force posted an image on Twitter of a protester on top of a bus on Whitehall, and confirmed that he was “now down safely”.
Responding to social media posts saying Islamic State flags were carried in the crowd, the Met said that specialist officers had confirmed that these were the “shahada”, a declaration of faith in Islam.
The platform at Marble Arch tube station was briefly closed because of the crowds.
The gathering took place as the Rafah border crossing was opened on Saturday, allowing a trickle of humanitarian aid to pass from Egypt into Gaza after a week of intense negotiations involving the US, Israel, Egypt and the UN.
The shipment of 20 trucks bringing medical supplies offered limited relief to Gaza’s 2.3 million population, under fire and with barely anything to eat or drink. The UN secretary general, António Guterres, said “much, much more” is needed.
In London, some of the protesters chanted, “From the river to the sea, Palestine will be free”, despite a controversy around the slogan’s meaning.
The home secretary, Suella Braverman, has previously labelled the slogan antisemitic and claimed that it is “widely understood” to call for the destruction of Israel. Jewish groups have asked prosecutors to clarify whether chanting the slogan is a criminal offence.
However, the slogan’s defenders describe it as a “longstanding protest chant” that calls for a homeland for the Palestinian people.
The Met has said that although the chant could be unlawful outside a synagogue or Jewish school, or addressed directly to a Jewish person, “its use in a wider protest setting, such as we anticipate this weekend, would not be an offence and would not result in arrests”.
A small group of protesters held a separate demonstration in central London on Saturday in which a large banner read: “Muslim armies, rescue the people of Palestine.”
Speakers addressed the group of about 100 people in Arabic as they gathered in Balfour Mews, just off the path of the main protest.
The Met said it was deploying 1,000 officers to police the demonstration, as well as mounting extra patrols around synagogues and places of worship after a 1,350% increase in hate crimes against Jewish people and a 140% rise in Islamophobic incidents.
The Met said there had been “pockets of disorder and some instances of hate speech” in the series of vigils, protests and public gatherings, but that most had “been lawful and taken place without incident”.
Before the march on Saturday, the largest had been a week before, at which 15 arrests were made, the Met said.
The war has sparked pro-Palestinian and pro-Israeli protests around the world. In Australia, thousands marched through central Sydney after police gave the event the green light, and rallies were also held in Perth, Hobart and Brisbane.
Several hundred people also marched in the Italian capital, Rome, and protests were held in New York. Police in Berlin have banned a pro-Palestinian rally on Sunday.