Iran is seeking to expand its hostile operations in Britain to more heavily protected targets, including military installations, the head of MI5 has warned.
Sir Ken McCallum, Director General of the Security Service, delivered the warning in his annual threat update at Thames House on Tuesday 13 October 2026, describing a changing national security environment in which hostile states increasingly rely on intermediaries to carry out intimidation and sabotage.
Iranian threat moving towards military sites
Sir Ken said MI5 continued to see Iranian-linked attempts to intimidate opponents of the Iranian authorities, Iranian media organisations and Israeli-linked sites. However, he identified a further development in 2026: attempts to reach more difficult targets, including military facilities.
He said MI5's Iran-linked operations had led to more than 50 arrests in the UK over the previous 12 months. That figure describes arrests connected with investigations, not convictions or proof that every arrested person acted on instructions from Tehran.
The MI5 chief also highlighted attacks against Jewish communities and referred to two Iranian nationals charged with terrorism offences following an alleged plot targeting the Jewish community in Manchester. Criminal allegations remain subject to the courts.
RAF Fairford investigation
The warning follows a security operation near RAF Fairford in Gloucestershire in September. Seven men were arrested and subsequently released on bail while investigations continued, according to contemporary reports. The airbase has been used by US military aircraft.
Asked about the incident following his speech, Sir Ken said it was not unique and pointed to other examples of attempts against military targets internationally. He declined to discuss the details of the live investigation, citing the risk of prejudicing any future prosecution.
Authorities have examined possible Iranian involvement, but that assessment should not be confused with a judicial finding about who directed the suspected plot. Iran has denied involvement in hostile activity in Britain.
Russia and wider state threats
Sir Ken also warned that Russia was intensifying hybrid operations against Britain and its allies, including efforts to recruit intermediaries for sabotage. He said MI5's state-threat workload had quadrupled over the past decade and that the service was now devoting more resources to countering state threats than during the Cold War.
His address also raised concerns about terrorists exploiting artificial intelligence, particularly in support of reconnaissance and the development of biological threats.
What happens next?
MI5's warning reflects an intelligence assessment of evolving threats rather than an announcement of new criminal charges or evidence of an imminent attack at a particular military base. The RAF Fairford investigation remains a separate live matter, and those involved are entitled to the presumption of innocence.