Chanting "Free Palestine", holding banners and waving Palestinian flags, the protesters moved through London before massing at Downing Street, the official residence and office of British Prime Minister Rishi Sunak.

Police estimated 100,000 people had taken part in the "National March for Palestine" demonstration, organised by the Palestine Solidarity Campaign.

"As a Palestinian who'd like to return home one day, as a Palestinian who has brothers and sisters in Gaza, and family, I wish we can do more but protest is what we can do at the minute," one woman, who declined to giver her name, told Reuters.

Many of the chants and banners contained strong anti-Israeli slogans, and one protester held a banner with pictures of Sunak, U.S. President Joe Biden, and Israeli Prime Minister Benjamin Netanyahu with the message "Wanted For War crimes".

Police had cautioned before the march that anyone showing support for Hamas, banned as a terrorist organisation in Britain, would face arrest, and any incident of hate crime would not be tolerated.

The protest appeared peaceful and there were no immediate reports of any arrests.

Figures on Friday showed there had been a 1,353% increase in antisemitic offences this month compared to the same period last year, while Islamophobic offences were up 140%.

"This has been an issue which has long stimulated passions and we are now all seeing on social media and in our communities, how divisive and polarising the current situation has become," British foreign minister James Cleverly said at a peace summit in Cairo.