The head of MI5 has warned that the security services do not yet know what long-term impact coronavirus will have on terrorist threats to Britain.

Ken McCallum, who became director-general of MI5 at the start of the pandemic, said it had been a “mixed phenomenon” with both positive and negative effects on national security.

In his first interview, Mr McCallum said lockdowns had left extremists to get “even more sucked into” terrorist ideologies online, while “stewing in their bedrooms”.