MI5 has shifted resources to counter state threats at Cold War-scale intensity, with the agency now devoting equal effort to terrorism and foreign adversaries combined, the head of the intelligence service said.
Sir Ken McCallum told an audience at MI5 headquarters in London that threats from foreign states had quadrupled over the past decade. Russia ranks as "aggressor number one", he said, conducting hybrid warfare against UK targets including cyber-attacks, sabotage and disinformation while stopping short of direct military conflict with NATO.
The MI5 chief said Russian spy expulsions numbering nearly 1,000 since the Ukraine invasion have weakened Moscow's covert footprint, forcing the Kremlin to pay criminal proxies for attacks. He rejected suggestions this represents strength: "These are not the actions of a great power with the strategic upper hand."
Iran has expanded hybrid operations within the UK, McCallum added, with 50 arrests made in the past year over Iran-linked activities. Much targeting has focused on Jewish communities and military sites. He did not directly name the July 2024 incident at RAF Fairford in Gloucestershire, where seven people were arrested after suspicious vans appeared near the airbase, but confirmed the intelligence service has observed wider Iranian interest across UK military installations.
On artificial intelligence, McCallum warned the technology amplifies threats on multiple fronts. Extremist groups have used AI to enhance reconnaissance and attack planning, including integration with drones. The most serious emerging risk involves potential bioweapon development, though he stressed this threat has not yet materialised.
MI5 has launched an AI Threat Assessment Centre to distinguish genuine risks from speculation. McCallum acknowledged the uncertainty: "Human history has given us no experience of facing an actor which is smarter than we are."
Terrorism threat levels remain elevated. In April, the UK's official terrorism threat level rose to severe, the first such rating in five years. McCallum identified extreme right-wing terrorism as driving much recent growth, with investigations spanning ages from adults down to a radicalised 13-year-old identified in recent months. Islamist groups including Al Qaeda and Islamic State continue directing attacks.
Questioned on Russian interference in the 2016 Brexit referendum, McCallum acknowledged Russian media and "internet trolls and bot farms" attempted to influence the debate but cautioned against overstating impact: the referendum result remains undisputed. He expressed concern that focusing on such interference plays into adversaries' hands by inflating their perceived influence.
The 2023 National Security Act, designed to prosecute those working for foreign powers against UK interests, is being "heavily used", McCallum said, targeting Russian, Iranian and Chinese operations.