In My Day They Would All Have Been Arrested (Kettled) To Prevent Breach Of The Peace.

https://news.sky.com/story/israel-hamas-war-from-the-river-to-the-sea-controversial-chant-heard-as-thousands-join-pro-palestine-march-in-london-12994655

Then individually searched, identified and photographed.

Only being released once it had been established that hadn't committed/aren't wanted for any offence.

Crimes Against Humanity certainly aren't covered by; "Freedom of Expression."

https://twitterwithbraincells.blogspot.com/2023/10/the-prosecutor-of-special-court-vs.html