Britain now devotes more counterintelligence resources to state-level threats than it did during the Cold War, according to Sir Ken McCallum, head of MI5. Speaking at the domestic intelligence service’s headquarters in London, McCallum called Russia “aggressor number one” and warned that threats from foreign adversaries had quadrupled. MI5’s terrorism and state-threat missions now operate on “pretty much of equal scale,” he said.
Britain’s security priorities have been reordered. For decades, officials assumed terrorism posed the dominant threat to European nations. That calculation has flipped. Russia’s hybrid warfare campaign across Europe, Iranian espionage networks targeting Jewish communities and military sites, and AI-enabled attack methods have pushed intelligence services to shift resources at a pace unseen since the Soviet Union collapsed.
The Russian Dimension
McCallum described Russia’s progress in Ukraine as “minimal and horrifically costly.” Yet Moscow continues its hybrid campaign across Europe, taking care to avoid direct military confrontation with NATO. The Kremlin, he said, would be “foolish to cross” the line into conventional conflict with the alliance. This approach—aggression without escalation—demands sustained, expensive counterintelligence work.
Since the invasion, Britain has expelled nearly 1,000 Russian spies, weakening Moscow’s traditional covert capacity. But that damage hasn’t eliminated the threat. McCallum said the Kremlin now pays criminals to carry out proxy operations. “These are not the actions of a great power with the strategic upper hand,” he said. His comment carries weight: it suggests Russia’s intelligence apparatus, once the KGB and now the FSB, has retreated strategically on British soil.
Emerging Threats and Technological Risk
McCallum warned that Iran has expanded its hybrid campaign in the UK. Authorities have made 50 arrests related to Iran-linked activities in the past year, much of it involving targets in Jewish communities and at military and strategic facilities. Alongside the Iranian threat, McCallum identified what may be the most pressing emerging risk: extremist groups bringing artificial intelligence into attack planning.
MI5 has already caught terrorists trying to use AI to improve reconnaissance and attack methods, including the development of AI-enabled drones. McCallum said his greatest concern was extremist groups using AI to develop bioweapons. “The threat is not yet realised,” he cautioned, “but the technology has the potential to change the stakes on existing or even new bioweapons.” MI5, GCHQ, and MI6 are working with the UK’s AI Security Institute to address these risks.
The Domestic Terrorism Rebalance
In April, the UK raised its terrorism threat level to severe for the first time in five years, meaning an attack was highly likely. Islamist groups including Al Qaeda and so-called Islamic State continue to direct and inspire attacks. McCallum also pointed to a distinct trend: more cases in which extremist anti-immigration and anti-Muslim grievances tip into terrorist intent.
Extreme right-wing terrorism tends to “skew young,” McCallum said, and internet radicalization drives it. MI5 recently investigated a radicalized extreme right-wing 13-year-old in the UK. That inquiry produced intelligence that enabled an international partner to prevent a lethal attack on their soil. The threat’s youth-skewing suggests it isn’t a passing phenomenon; it’s embedded in the digital native generation.
Legal Tools and Enforcement
Enacted in 2023, the National Security Act has become a frequently used tool against state-sponsored threats. McCallum said the agency has used it to tackle threats from China, Iran, and Russia. The law targets people working against UK interests for foreign powers, covering traditional espionage as well as the proxy networks Russia assembled after losing its conventional spy footprint in Britain.
Why This Matters:
MI5’s shift in resources from terrorism to state threats carries serious implications for European security and defense spending. If Britain’s domestic intelligence service now devotes as much effort to Russian, Iranian, and Chinese state activities as it does to jihadist terrorism, that points to a wider strategic reality: great-power competition has returned to the center of Europe. The shift has fiscal consequences. States can’t maintain security indefinitely on budgets built for counterterrorism alone. Britain will need to fund its intelligence services accordingly, and European allies face the same pressures. McCallum’s speech also exposes a vulnerability: Russia still conducts hybrid warfare despite near-total intelligence expulsion, relying on paid proxies and criminal networks. That persistence, combined with the emerging risk of AI-weaponized bioterrorism, suggests threats aren’t stabilizing; they’re splitting into multiple, simultaneous risks that no single agency can handle alone. European coordination on intelligence-sharing and AI security will become essential, but only if member states commit resources and share information more effectively than Brussels-level initiatives have historically managed.