Christopher Lythgoe, leader of the proscribed group National Action, has been jailed for eight years

Counterterrorism police threatened to arrest anti-fascist activists who alerted them to a far-right plot to murder an MP, it was claimed last night.

A Metropolitan Police officer told Hope Not Hate campaigners they had breached anti-terrorism legislation by “running” an informant in the proscribed organisation National Action.

The inside man had tipped them off about a plan to kill the Labour MP Rosie Cooper by a member of the group, Hope Not Hate told The Times.

Nick Lowles, the chief executive of Hope Not Hate, accused Scotland Yard’s counterterrorism command of a “bullying, threatening” approach.

Ms Cooper, 67, the MP for West Lancashire, who was in court yesterday to see two men sentenced for being members of National Action, thanked Robbie Mullen, Hope Not