MI5 warns of growing security threats to Britain
McCallum described Russia as the UK’s leading state-based aggressor, accusing Moscow of intensifying hybrid warfare against Britain and its allies. These activities include cyberattacks, sabotage, surveillance and attempts to incite violence, often designed to remain below the threshold for a direct military response.
Russia’s capabilities have been affected by the expulsion of around 1,000 diplomatic officials from embassies since its invasion of Ukraine. Moscow has consequently relied more heavily on local recruits and criminal intermediaries to carry out hostile activities. Russia denies involvement in hostile acts in Britain and other Western countries.
Iran expands operations against British targets
Iran has also emerged as a growing concern, with MI5 warning that Tehran is seeking to expand its operations beyond targeting political opponents and Iranian media organisations. British Jewish communities and Israeli interests have also faced alleged threats linked to Iranian proxies.
According to some media reports, Iran-linked operations resulted in more than 50 arrests in the UK over the preceding 12 months. McCallum highlighted a shift towards more ambitious targets, including military installations.
The warning follows a suspected plot involving RAF Fairford, a US-operated military airbase in western England. The incident triggered a security response in September, with seven men arrested and later released on bail under investigation, according to the Associated Press. Police reportedly found petrol in three vans but no explosives.
McCallum said the incident was not unique, although he declined to comment in detail because investigations were continuing. Iran has rejected allegations of involvement and demanded evidence from Britain.
AI and terrorism add to security concerns
Artificial intelligence is another major concern for MI5. McCallum said the technology was strengthening both cyber attackers and defenders while allowing hostile actors to create targeted propaganda and improve reconnaissance and attack planning.
He warned that terrorists could potentially use AI to access dangerous biological knowledge or develop previously unknown pathogens. AI-enabled drones have also introduced new challenges for security agencies.
To address these risks, MI5 launched an AI Threat Assessment Centre in 2026. The centre brings together expertise from bodies including the AI Security Institute, the National Crime Agency, and the National Cyber Security Centre.
Domestic terrorism remains a serious concern. The UK raised its national terrorism threat level from substantial to severe in May 2026, meaning an attack was considered highly likely. Islamist extremism remains the primary threat, while extreme right-wing terrorism is also increasing.
McCallum also warned that online radicalisation, including among young people, could turn extremist views into violence. He called for a broader national response, arguing that protecting Britain's security would require cooperation beyond intelligence agencies alone.