Police arrested an activist on suspicion of supporting a banned organisation as thousands of pro-Palestinian protesters prepared to march near to the Israeli embassy on Saturday.
Scotland Yard said the arrest had been made “on suspicion of support for a proscribed organisation in relation to a placard”.
Between 200,000 and 250,000 people were expected to gather for the demonstration, according to a spokesman for the Palestine Solidarity Campaign, which kicked off at 1.30pm near Marble Arch.
Many of the protesters held placards proclaiming: “From the river to the sea, Palestine will be free”, which is widely seen as a call for the destruction of the state of Israel.
Others brandished banners accusing Israel of genocide.
There were also claims that some of the marchers held placards with symbols showing support for Hamas gunmen, such as one appearing to show a V on a red background in imitation of the terror group’s red triangle symbol.
Around 1,500 police officers from forces across the UK are set to be on public order duties during the demonstration.
Activists were massing close to the Israeli embassy in Kensington for the second time since the October 7 attacks launched on southern Israel by Hamas.
The Met Police intervened to prevent the march starting until after a religious service at a synagogue along the route had concluded – although hundreds of pro-Palestine activists gathered nearby before the demonstration set off.