London’s streets have become a “no-go zone for Jews” during pro-Palestinian protests, the Government’s counter-extremism tsar warned.

Robin Simcox said a “permissive environment for radicalisation” was developing as he welcomed the Government’s forthcoming new definition of extremism.

Writing in The Daily Telegraph newspaper he said the Government should be prepared to “move faster” and “be bolder” in taking action against groups even if that meant a “higher legal risk”.

Mr Simcox, the commissioner for countering extremism, said “we will not have become an authoritarian state if London is no longer permitted to be turned into a no-go zone for Jews every weekend”.

His comments followed Prime Minister Rishi Sunak’s promise to deal with the “root causes” of the problem and ensure that “no extremist organisations or individuals are being lent legitimacy by their actions and interactions with central government”.

A definition of extremism, expected to be set out by Communities Secretary Michael Gove as soon as next week, could ban Government officials from engaging with or funding groups or individuals deemed extremist.

But it has led to concerns from some on the right that it could inadvertently penalise groups opposed to gay marriage, abortion or new transgender rights.

Mr Simcox said: “While debates over a definition can feel like academic navel-gazing when actual extremist acts are so common, the work does have a clear purpose: it will be used to guide future decisions over who Government does, and does not, engage with and fund.

“The Government is right to act. Evidence that the state works with or funds extremists has appeared in independent reviews or Government strategies dating back over a decade. This needs fixing, new definition of extremism or not.”

He suggested the Government and its agencies already powers to combat extremism but had failed to tackle groups that fall below the threshold of being terrorists.

He said Whitehall “has more power to tackle extremism than it sometimes thinks”.

“After all, the Iranian government does not have an inalienable right to run schools and mosques in our capital city.

“It is not an unalterable democratic principle that Hamas and the Muslim Brotherhood must be allowed to run a multitude of charities,” he said.

“We have not betrayed democracy if extremists are no longer able to operate television channels.”