Britain's domestic intelligence agency now devotes more resources to countering state threats than it did during the entire Cold War, according to Sir Ken McCallum, head of MI5. Foreign state threats have quadrupled, and Russia has become what McCallum calls “aggressor number one.”
In his annual address at MI5's London headquarters, McCallum described a security environment reshaped by hybrid warfare, authoritarian aggression, and the weaponization of new technologies. Liberal democracies, he argued, need more than reactive counter-intelligence; they must rethink how to defend themselves as the traditional lines between war and peace blur.
The moment stands apart for more than the return of great-power competition. State-sponsored threats now converge with rising extreme right-wing terrorism at home, creating a dual security challenge that tests democratic societies.
The Russian Threat and the Limits of Hybrid Warfare
Russia has abandoned traditional espionage in Britain. McCallum said nearly 1,000 Russian spies have been expelled from the UK since the invasion of Ukraine, decimating the Kremlin's “traditional covert footprint.” Moscow now relies on paid proxies and criminal networks to carry out operations.
“These are not the actions of a great power with the strategic upper hand,” McCallum said, describing Russia's tactics as desperate scrambling masked by aggression. Russia continues what he called “hybrid warfare,” deliberately stopping short of conventional conflict that would trigger a unified NATO response. McCallum warned that crossing that line would be “foolish.”
Meanwhile, Russia's full-scale invasion of Ukraine continues at a horrific cost. McCallum called the Kremlin's progress “minimal and horrifically costly,” describing a strategic failure accompanied by immense human suffering.
The UK's counter-intelligence campaign has proved remarkably effective. But McCallum's assessment also exposes the limits of security services acting alone. Russia's reliance on proxies and criminal networks shows why counter-espionage, necessary as it is, can't resolve the geopolitical competition behind state threats. That takes sustained diplomacy, coordination among allies, and continued support for Ukraine—security work well beyond intelligence agencies.
Iran's Expanding Campaign and Targeted Violence
Iran has significantly expanded its hybrid operations in the UK. Over the past year, authorities have made 50 arrests linked to Iran-related activity. McCallum said much of this aggression has targeted Jewish communities, as well as military and other strategic targets.
Enacted in 2023, the National Security Act has become a critical tool against these threats. The law targets individuals working against UK interests on behalf of foreign powers, and authorities have used it heavily against operations linked to China, Iran, and Russia.
The Acceleration of Extreme Right-Wing Terrorism
Perhaps the most alarming part of McCallum's remarks concerned the course of extreme right-wing terrorism in Britain. In April, the UK raised its terrorism threat level to severe for the first time in five years, meaning an attack was considered highly likely. Islamist groups, including Al Qaeda and Islamic State, still direct and inspire attacks, but McCallum said the increased risk now comes “in significant part” from extreme right-wing terrorism.
The trend is clear. “Over the last year the most marked trend has been an increase in cases where extremist versions of anti-immigration and anti-Muslim grievance are tipping into terrorist intent,” he said.
Intelligence agencies can't solve this challenge alone. Extreme right-wing terrorism tends to “skew young” and is driven mainly by the internet. MI5 recently investigated a radicalized 13-year-old in the UK who held extreme right-wing views. The investigation prevented harm, but it also points to the scale of online radicalization affecting Britain's children.
The AI and Bioweapons Frontier
McCallum warned about emerging technologies that could have apocalyptic consequences. MI5 has already caught terrorists trying to use artificial intelligence to improve reconnaissance and attack methods, including by combining AI with drone technology.
His gravest concern, though, is extremist groups using AI to develop bioweapons. “The threat was ‘not yet realised,’ he said, but the technology had the ‘potential to change the stakes on existing or even new bioweapons.’” The UK Intelligence Community—MI5, GCHQ, and MI6—is working closely with the UK's AI Security Institute to address the risks.
The warning reflects a security environment where asymmetric threats multiply faster than traditional defenses can adapt. Britain's intelligence services and their international partners are racing to keep ahead as hostile actors learn to weaponize new technologies.
Why This Matters:
McCallum's assessment describes a democratic state under pressure from several directions. Russia's hybrid aggression, Iran's expanding operations, the surge in extreme right-wing terrorism, and the weaponization of AI and biotech technologies create threats no nation can manage alone. Britain has expelled Russian intelligence operatives, invoked the National Security Act, and coordinated with international partners to prevent attacks. Those steps have been necessary and, in many cases, effective.
Still, the forces behind these threats—geopolitical competition, online radicalization of young people, and the spread of dangerous technologies—demand more than counter-intelligence. They call for investment in integration, education, digital literacy, and international cooperation on security and diplomacy. The severe terrorism threat level, driven partly by anti-immigration grievance, also points to a social fracture that arrests alone can't seal. Liberal democracies must confront both the immediate threat and its roots: polarization, falsehoods about immigration and identity, and the feeling among some communities that no one hears them. That work belongs to governments, civil society, and European partners acting together—not intelligence agencies working alone.