The MI5 director general, Ken McCallum, has acknowledged his frustration at the failure to put on trial two Britons who had been accused of spying for China, in an apparent rebuke to prosecutors who dropped the high-profile case last month.
The domestic spy chief insisted he would “never back off” from confronting threats from Beijing, which he said posed a national security threat “every day”, although the wider UK-China relationship was a matter for the government.
