The Community Security Trust has welcomed plans for a new team of specialist police officers to target antisemitic trolls on the internet.

The £1.7 million London unit will be run by the Metropolitan Police and is backed by Sadiq Khan, the Mayor of London. It will attempt to tackle the increase in abusive messages sent on the internet and social media sites.

A CST spokesman said the idea had been developed over the past two years and had been made possible by a government grant. He added: "We are pleased this pilot is going to take place. We have discussed the project with the Metropolitan Police to see how we can help and will work with them to reduce antisemitism on social media."

A spokesperson for MOPAC - the mayor's office for policing and crime - said: "Community groups in London have told us that online hate crime is an issue of increasing concern to them, and one for which the police response has in the past been inconsistent."

But concerns have been raised that the unit could become a form of "thought police", with internet users' freedom of expression curtailed.

Tim Farron, Liberal Democrat leader, said police should not "proactively" turn themselves into "chatroom moderators".