Britain attributed a security incident that occurred the previous month at a base shared with American forces in southern England to Iran, subsequently summoning Tehran's ambassador and announcing sanctions targeting two named individuals. On 27 September, police took five people holding British passports into custody near RAF Fairford, with the detentions made under suspicion of offences related to terrorism and explosives. Bail was granted with a set of restrictive conditions attached, and a further arrest came within days.

Those leading the inquiry had already been examining whether a foreign state bore responsibility for the incident — a thread of investigation informed partly by RAF Fairford's function as a staging point for US Air Force activity across Europe, housing long-range aircraft including B-1s and B-52s, both types capable of reaching targets at considerable distance, among them locations within Iran.

A senior official stated that assessments pointed toward coordination originating from Iran, with direction attributed to the Islamic Revolutionary Guard Corps (IRGC), adding that such activities on home soil would not be accepted. Separately, how capable the group of young Londoners actually was, and the extent of any threat they posed, remained uncertain.

Early findings from the investigation pointed to an absence of functional explosive devices across the vans, even after a broad security alert had been raised and a bomb disposal team called in to examine them. Petroleum-based accelerants were among the substances recovered at the scene.

Speaking to the House of Commons on Monday, Andy Burnham stated that authorities would move against the networks Iran allegedly uses for criminal activity, deploying the full range of available powers to disrupt their financing, and that additional sanctions would be pursued to limit the capacity of both Iran and the IRGC to cause harm. Burnham also indicated that further sanctions against Iran remained a possibility under consideration.

On Monday, the Foreign Secretary summoned Iran's ambassador to restate Britain's position that attacks on its soil would not be accepted. The ambassador — identified in reports from Iran's state news agency as Ali Moussavi — flatly denied the accusations and called on the British government to produce supporting evidence if any existed. Separately, the Foreign Secretary announced that two individuals would face an immediate asset freeze, a travel ban, and disqualification from holding directorships.

The two individuals named were Ruhollah Bazghandi, described as heading counterespionage operations within the IRGC, and Shahram Ali Reza Tamarzadeh Jakki, identified as someone authorities believe acted as a facilitator connected to the Zindashti criminal network. The Foreign Secretary linked the sanctions to those individuals' roles in supporting or carrying out covert operations on Iran's behalf — activities aimed at threatening, planning, or executing attacks in other countries.

Shortly after that announcement, a joint statement bearing the endorsement of 29 nations set out a collective objection to Iran's use of violence beyond its borders, characterising the conduct as spanning lethal plotting, arson, sabotage, cyber operations, and other hybrid activities directed at the signatory states and their partners. Among the countries whose names appeared on the document were the United States, Britain, Australia, Canada, France, Germany, Spain, and Ireland, a roster that included the Five Eyes intelligence-sharing grouping alongside the bulk of European NATO membership.

Following the incident recorded on 27 September at Fairford, the American B-1 bombers were withdrawn from the base. A formation of B-52s — the older models and the greater share of the fleet — held its position at that location.

Among the airbases in southern England, RAF Fairford is one of a handful that host a substantial American military presence and operational footprint. Sitting roughly two hours by road to the west of London, the site occupies a patch of countryside just north of Swindon.