Britain's domestic intelligence agency MI5 says its workload involving hostile foreign states has quadrupled over the past decade, as Russian and Iranian operations, persistent terrorism threats and emerging artificial intelligence capabilities place growing demands on national security.
MI5 Director General Sir Ken McCallum delivered the assessment on October 13, 2026, at the agency's London headquarters, Thames House. He said MI5 now devotes more resources to countering state threats than it did during the Cold War, while counterterrorism and state-security work occupy roughly equal shares of its operational effort.
The warning accompanied significant organizational changes, including the elevation of national resilience to a third core mission and the creation of a dedicated center to assess AI-related security risks.
Why MI5 Says State Threats Have Quadrupled
In his annual threat assessment, McCallum described a fundamental change in Britain's security environment, with intelligence officers confronting overlapping threats from foreign governments, terrorist organizations and increasingly accessible technologies.
The fourfold increase refers specifically to MI5's state-threat caseload over ten years. It does not mean that confirmed foreign-state attacks have increased by the same proportion. Intelligence cases can involve suspected espionage, hostile surveillance, attempted interference, sabotage planning and other activities that never result in a completed attack.
McCallum also highlighted the growing use of Britain's National Security Act, which has supported dozens of arrests since coming into force in 2023. He said prosecutions and convictions have involved activity connected to Russia, Iran and China.
The Cold War comparison is particularly significant because countering Soviet intelligence once dominated much of Britain's domestic security work. MI5's current assessment suggests hostile-state activity has again become a central operational priority, even as the agency continues to investigate terrorism.
Russia and Iran Dominate Foreign-State Security Concerns
McCallum identified Russia as Britain's leading state-security adversary, accusing Moscow of intensifying hybrid operations against the United Kingdom and its allies.
Hybrid warfare can encompass sabotage, cyberattacks, covert influence campaigns and operations conducted through intermediaries. Such activities can create serious disruption without necessarily involving an openly declared military confrontation.
British intelligence officials say Russia has increasingly relied on proxies and unconventional methods as Western governments have restricted the operations of suspected Russian intelligence personnel. Nearly 1,000 Russian diplomatic personnel were expelled internationally following Moscow's full-scale invasion of Ukraine in 2022, according to McCallum. That figure represents action across multiple countries, not expulsions by Britain alone.
The assessment comes amid broader European concern about Russia's military and unconventional activities, including NATO's evolving strategy for countering Russian threats. Russia has denied responsibility for hostile operations attributed to it by Western governments.
Iran presents a different but increasingly prominent challenge. McCallum said more than 50 arrests had been made in Britain over the preceding 12 months in connection with investigations involving Iranian-linked activity.
He warned that suspected Iranian operations were expanding beyond longstanding targets, including dissidents and Jewish or Israeli interests, toward more heavily protected locations such as military facilities.
One prominent example is the investigation into a suspected plot involving RAF Fairford, a military air base in western England used by US forces. Following an incident on September 27, police arrested seven men who were subsequently released on bail while the investigation continued.
As BBC News reported in its coverage of the intelligence warning, concerns about foreign-state activity now extend beyond traditional espionage into potential physical attacks and disruption.
British officials have alleged Iranian involvement in the Fairford incident, but that allegation must be distinguished from an established judicial finding. Iran denies involvement and has demanded evidence supporting the accusations. According to Associated Press reporting, Tehran also protested the British allegations through diplomatic channels.
Neither the arrests nor the intelligence assessment establishes the guilt of individual suspects or conclusively proves who directed the suspected operation.
Terrorism Remains a Major Threat to Britain
Despite the increased emphasis on hostile foreign governments, MI5 continues to regard terrorism as a major national security concern.
McCallum highlighted persistent Islamist terrorist activity and a concerning increase in extreme-right-wing terrorism investigations. He also raised concerns about young people becoming involved in violent extremist activity through online radicalization.
On April 30, 2026, Britain's Joint Terrorism Analysis Centre raised the national terrorism threat level from SUBSTANTIAL to SEVERE following an antisemitic attack in north London and a broader assessment of terrorist risks.
The UK government's published threat-level guidance defines SEVERE as meaning a terrorist attack is considered highly likely. The designation remained in place as of October 14, 2026.
This formal assessment concerns terrorism and should not be confused with MI5's separate evaluation of foreign-state threats. Although the two areas can overlap, they involve different intelligence assessments, legal considerations and potential perpetrators.
The Home Office's April announcement also outlined additional protective security measures for Jewish communities and proposed stronger tools against organizations conducting hostile activity on behalf of foreign states.
MI5 Expands Protection Efforts and Creates AI Threat Centre
One of the most consequential elements of McCallum's announcement was the elevation of Protect to a third core MI5 mission, alongside counterterrorism and countering state threats.
Protect focuses on strengthening Britain's ability to withstand hostile activity. This includes improving the security of critical infrastructure, supporting organizations facing national security risks and helping essential services continue operating during serious disruptions.
The change does not mean protective security is entirely new to MI5. Rather, the agency is formally giving resilience a more prominent role in its overall mission, reflecting the wider range of threats confronting the country.
McCallum also announced the launch of the AI Threat Assessment Centre, known as AITAC.
The center brings together expertise from MI5 and other British organizations, including the AI Security Institute, National Crime Agency and National Cyber Security Centre. Its purpose is to assess emerging AI-related threats and help officials distinguish credible dangers from exaggerated claims.
McCallum warned that artificial intelligence could enhance cyberattacks, assist hostile reconnaissance and potentially make sophisticated capabilities more accessible to malicious actors. He also identified possible future risks involving biological weapons, including AI-assisted access to dangerous scientific knowledge.
These concerns require careful interpretation. The possibility that AI could contribute to biological-weapons development does not establish that a terrorist organization has successfully created or deployed such a weapon using AI.
Similarly, establishing an assessment center does not itself demonstrate that the government can prevent every emerging technological threat. Its effectiveness will depend on intelligence quality, technical expertise, coordination and the ability to respond as technologies evolve.
What MI5's Warning Means for UK Security
The central message of McCallum's assessment is that British national security can no longer be understood primarily through the separate categories of terrorism and traditional espionage.
Hostile-state operations can involve criminal intermediaries, digital disruption, threats to military facilities and attempts to undermine essential services. At the same time, terrorist groups and individual extremists may gain access to technologies that make planning, recruitment or reconnaissance easier.
For British authorities, the challenge is therefore twofold: identifying and disrupting dangerous activity while making important institutions and infrastructure more resilient if an incident occurs.
MI5's expanded protective mission also places greater importance on cooperation among intelligence agencies, law enforcement, businesses, infrastructure operators and international partners.
Nevertheless, significant uncertainties remain. The full scale of clandestine foreign-state activity is not publicly measurable, some prominent investigations have yet to establish responsibility, and the practical consequences of AI advances remain difficult to predict.
McCallum's October 13 warning is therefore best understood as both an assessment of growing intelligence demands and an explanation of why MI5 is changing how it protects Britain. Whether those changes substantially reduce future risks will depend on developments that cannot yet be measured from the public record.
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