LONDON — The threat from states such as China is as bad or worse as the threat of terrorism, the head of one of Britain’s top intelligence agencies warned Thursday.

Giving his annual threat update speech from MI5 headquarters at Thames House in London, MI5 director general Ken McCallum called for the most profound change in the way British intelligence operates “since 9/11.”

His comments come as Westminster continues to be engulfed by questions over the high-profile collapse of a case against two alleged Chinese spies. Both the British government and the Crown Prosecution Service (CPS) have faced scrutiny over the case after the CPS unexpectedly dropped the charges against the two men in question last month.

Speaking Thursday, McCallum said his teams are running a “near-record” volume of investigations into terrorism, and have foiled 19 late-stage terrorism attacks since 2020.

But he said that threats from states — including China — are now a “second menace of equal or even greater scale,” forcing “the biggest shifts in MI5’s mission since 9/11.”

McCallum said that since his update last year state-based threats to the U.K. are “escalating,” with an increase in the number of people being investigated for state threat activity — such as espionage “against our Parliament.”

Frustrated the case collapsed

Christopher Cash, 30, a former researcher for a Conservative MP, and Christopher Berry, a 33-year-old teacher, both denied allegations that they passed sensitive information to an alleged Chinese intelligence agent between 2021 and 2023. On Wednesday evening the British government published key witness statements from Matthew Collins, the deputy national security advisor, whose evidence was blamed by CPS for not providing enough grounds to prosecute the two men accused of spying for Beijing.

Asked how he felt about the collapse of the China prosecution against the two men, McCallum said: “Of course I am frustrated when opportunities to prosecute national security-threatening activity are not followed through.”

He added that in this specific event “the activity was disrupted” by MI5 and that his teams have “every right to feel proud” of the work they have done in the case. However he said that it is “far from unprecedented” for his officers to disrupt a threat to national security and for it not to result in a criminal conviction.

Asked about Collins, the deputy national security advisor who submitted the witness statements to the CPS, McCallum said he would make a “rare exception” to speak about Collins’ integrity, having worked with him. “I do consider him to be a man of high integrity and a professional of considerable quality,” he said.

McCallum was also careful not to criticize the work of the CPS, telling journalists: “Not only am I not a criminal prosecutor, I’m not a lawyer. And so for the same reason that the DPP (Director of Public Prosecutions) presumably wouldn’t stand up and comment on how to run covert intelligence operations, I’m not going to presume to appoint myself a temporary expert in the running of prosecutions.”

The decision to replace Britain’s Official Secrets Act with a new National Security Act — pointed to by the current Labour government as a key reason the case collapsed — was praised by McCallum, who said it has “definitely has closed serious weaknesses that we have previously suffered from.”

China a wider threat

The MI5 head said the relationship between Britain and China is “complex,” but his agency’s role “is not,” adding that the U.K, needs to become a “hard target” to “all the threats, including China, but not limited to China.”

McCallum revealed that in the last week MI5 had “intervened operationally” against China, though this is not believed to be related to alleged spying on Parliament by Beijing.

“Do Chinese state actors present a U.K. national security threat? And the answer is, of course, yes they do, every day,” he said. However, the MI5 chief would not “comment on the overall balance of U.K. bilateral foreign policy relationships with China.”

“When it comes to China the U.K. needs to defend itself resolutely against security threats and seize the opportunities that demonstrably serve our nation,” he added, pointing that the U.K. and its Five Eyes allies including the U.S. share a “pragmatic approach” and that having a “substantive relationship with China” means Britain is in a “stronger position from which to push back.”