Britain’s security landscape has taken center stage this week, as the head of MI5, Sir Ken McCallum, issued an extraordinary public warning about the daily threat posed by China. His remarks, delivered at MI5’s London headquarters on October 16, 2025, come hot on the heels of a collapsed espionage case involving two British men accused of spying for Beijing—a case that has since spiraled into a political storm, raising tough questions about the government’s ability to balance national security and international diplomacy.
“Do Chinese state actors present a UK national security threat? The answer is of course yes, they do every day,” McCallum declared to reporters, as cited by AP and Sky News. He revealed that MI5 had intervened to disrupt a Beijing-backed threat as recently as the past week, underscoring the immediacy and persistence of the challenge. According to McCallum, these threats range from cyberespionage and technology theft to covert interference in UK public life—efforts that MI5 agents are constantly working to uncover and neutralize.
This stark warning arrives amid the fallout from the abandoned prosecution of Christopher Berry, a teacher, and Christopher Cash, a former parliamentary researcher. Both men were charged under the Official Secrets Act last year, accused of providing information to China that could have harmed the UK’s interests. But just before their trial was set to begin in September 2025, the Crown Prosecution Service (CPS) dropped the charges. The reason, according to Director of Public Prosecutions Stephen Parkinson, was that government officials had refused to testify under oath that China posed a national security threat at the time of the alleged offenses, which spanned from 2021 to 2023.
Prime Minister Keir Starmer has denied any government interference in the case. In an attempt to push back against mounting criticism, the government released witness statements from Deputy National Security Advisor Matthew Collins on October 15, 2025. Collins described China as “the biggest state-based threat to the UK’s economic security” and noted that Beijing’s espionage activities “harm the interests and security of the UK.” The statements also detailed how Chinese intelligence services conduct “large-scale espionage operations” against the UK, threatening the country’s economic prosperity, resilience, and the integrity of its democratic institutions.
Despite these strong words, the collapse of the case has left both government officials and opposition politicians pointing fingers. The Conservative opposition accused the Labour government of failing to provide crucial evidence to prosecutors, suggesting the decision was motivated by a desire to protect the UK’s trading ties with China. Ministers, meanwhile, insisted that the evidence provided was sufficient and that the CPS made its decision independently. The Chinese Embassy, for its part, has called the allegations against Berry and Cash “malicious slander” and dismissed the UK’s concerns as “unfounded accusations that are purely fabricated and groundless.”
For MI5, the frustration is palpable. “Of course I am frustrated when opportunities to prosecute national security-threatening activity are not followed through, for whatever reason,” McCallum admitted, as quoted by The Independent. He was quick to add, however, that “in the particular case… the activity was disrupted,” emphasizing that MI5’s operational success is not always reflected in courtrooms.
The scale of the challenge facing British intelligence is formidable. McCallum reported a 35% increase in the number of people under investigation for espionage and state-sponsored threats in the past year alone, including cases targeting Parliament, universities, and the country’s critical infrastructure. The threat isn’t limited to China: Russia and Iran are also in the “big three” of hostile states, with MI5 and the police disrupting a steady stream of Russian surveillance plots and more than 20 potentially lethal Iran-backed plots in the past 12 months. “State threats are escalating,” McCallum warned, noting the increasing use of “ugly methods” such as sabotage, arson, and even physical violence—tactics he said he had not seen before from foreign governments during his intelligence career.
Britain’s relationship with China, meanwhile, remains a delicate balancing act. On one hand, the Starmer government has expressed a desire to reset ties with Beijing after years of tension over spying allegations, human rights concerns, China’s support for Russia in the Ukraine war, and the crackdown on civil liberties in Hong Kong. On the other, MI5’s warnings—and the uproar over the failed prosecution—have fueled calls for a tougher stance. Housing Secretary Steve Reed’s recent decision to delay approval for a new Chinese “super embassy” near the Tower of London, amid fears it could become a hub for espionage, only adds to the sense of unease.
“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,” McCallum stated, as reported by The Independent. He highlighted China’s attempts at “clandestine technology transfer,” “harassment and intimidation of opponents” (including pro-democracy activists), and efforts to “interfere covertly in UK public life.” The intelligence chief was clear: “I am MI5 born and bred. I will never back off from confronting threats to the UK wherever they come.”
This week’s events have triggered broader institutional responses. The Joint Committee on the National Security Strategy has launched a formal inquiry into the collapse of the espionage case, with its chair, Matt Western, telling Parliament there are “clearly still many questions yet to be answered.” For his part, Prime Minister Starmer has sought to draw a line under the scandal, insisting he will “not stand for anyone being unfairly blamed” and defending the deputy national security adviser’s actions as being in line with the constraints imposed by previous government policy.
As for the accused, both Berry and Cash have denied any wrongdoing. Cash, in particular, has spoken out about the personal toll of the collapsed trial: “I wish to reiterate that I am completely innocent. Not just because the case against me was dropped, but because at no point did I ever intentionally assist Chinese intelligence,” he said. “I have not had the daylight of a public trial to show my innocence, and I should not have to take part in a trial by media.”
Experts caution against letting any single incident dictate the UK’s entire approach to China. Ben Bland, director of the Asia-Pacific programme at Chatham House, told The Independent that “espionage or any single espionage case is one thing but at any one time the challenge from China in terms of influence operations, espionage is going to be much bigger than any one case.” He added, “Our relationship with China both bilaterally and the way in which China affects the world and how that has a knock-on effect on the UK’s interests is so broad.”
As the inquiry gets underway and the government faces pressure to clarify its position, one thing is clear: the threats facing Britain are not going away. MI5’s chief has sounded the alarm, and the question now is how the UK will respond—both in its courts and on the world stage.
