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London’s police chief has said better laws are needed to police extremism, amid criticism over the force's handling of pro-Palestinian protests.
Demonstrations urging the British government to call for a ceasefire in the Israel-Gaza war have been growing in momentum.
Though they are mainly peaceful, concerns have been raised about potential expressions of support for Hamas and slogans deemed anti-Semitic from some of the demonstrators.
Metropolitan Police Commissioner Sir Mark Rowley said about 100 people had been arrested since the war began three weeks ago.
But Sir Mark said his officers are limited by legal definitions of extremism, and arresting people without cause could risk “inflaming” the situation with the protesters.
Speaking to Sky News, Sir Mark said he would support a review into the legal definition of extremism and how it should be policed.
“There is scope to be much sharper in how we deal with extremism within this country,” he said.
“The law was never designed to deal with extremism, there's a lot to do with terrorism and hate crime, but we don't have a body of law that deals with extremism, and that is creating a gap.”
Anti-Semitic incidents have increased by a factor of 14 since the war began, while crimes against the Muslim community have tripled, he added, while promising “many more arrests” in the coming weeks.
He said lawyers from the Crown Prosecution Service are working with the police to help identify offences.
Nine people were arrested in central London during a peaceful pro-Palestine demonstration attended by at least 100,000 people calling for a ceasefire.
Seven of the arrests were for alleged public order offences, a number of which are being treated as hate crimes, while two were on suspicion of assaulting officers.
Sir Mark said: “We've got these big protests and some of what goes on there, people do find it upsetting and distasteful and sometimes people give an instinctive view that must not be legal.
“But there's no point arresting hundreds of people if it's not prosecutable, that's just inflaming things.
“We will robustly enforce up to the line of the law. We're going to be absolutely ruthless and we have been and you'll see many more arrests over the next week or so.”
Levelling Up Secretary Michael Gove is understood to have ordered officials to draw up a new official definition of extremism in a move designed to counter hate, including anti-Semitism.
The Sunday Telegraph has reported that officials in the Department for Levelling Up, Housing and Communities are examining a suggested new definition of hateful extremism.
The work is understood to have started before violence flared up again in the Middle East.
Separately, the Home Office is examining potential changes to terrorism legislation, the newspaper reported.
A spokeswoman for the Department for Levelling Up, Housing and Communities declined to comment on Sir Mark's comments or the report.