The head of MI5 has said “Chinese state actors” present a national security threat to the UK “every day” and he admitted he was frustrated by the collapse of the case against two alleged Westminster spies. Sir Ken McCallum set out how the Security Service carried out an operation against a threat from China within the last week amid growing questions around the failure to prosecute.In a speech at MI5’s London headquarters, the service’s director general said that the UK needed to “defend itself resolutely” against China while also being able to “seize the opportunities” having a relationship with Beijing brings.“The UK-China relationship is, by its nature, complex, but MI5’s role is not: we detect and deal, robustly, with activity threatening national security,” Sir Ken said.He highlighted attempts by China to carry out “cyber espionage”, “clandestine technology transfer”, efforts to “interfere covertly in UK public life” and the “harassment and intimidation of opponents” including pro-democracy activists.“When it comes to China, the UK needs to defend itself resolutely against threats and seize the opportunities that demonstrably serve our nation,” he said.It was a choice for ministers to decide where the balance lies, he said, “informed by expert security advice”.Asked if he was frustrated by the collapse of the case against Christopher Cash and Christopher Berry, he said: “Of course I am frustrated when opportunities to prosecute national security-threatening activity are not followed through, for whatever reason.”Sir Ken’s comments came after it emerged the government’s deputy national security adviser had repeatedly described the “threat” posed by China in witness statements, published on Wednesday night, amid the extraordinary row over the collapse of the case.A key allegation against the government was that it refused in its evidence to the CPS to describe Beijing as a threat to Britain’s national security. MI5 chief Ken McCallum says he is ‘frustrated’ by the case collapsing More