The sixth arrest

The arrest is the sixth connected with events at the Gloucestershire airbase. Five men in their twenties, all UK nationals from London, were arrested in the early hours of Sunday after three suspicious vehicles were reported travelling towards the base, which is operated by the US Air Force and has been used as a forward operating location for US bombers for decades. They were detained on suspicion of explosives offences and later on suspicion of preparing to commit a terrorist act, before being released on police bail on Monday. Four live in Westminster and one in Camden, and searches of their homes were carried out. Police said a quantity of petrol but no explosive devices was found in vans near the site.

The BBC understands that one of the men dialled 999 himself, roughly an hour before a local farmer reported a large group of masked men near the vehicles.

Foreign state involvement in scope

Senior national coordinator Vicki Evans said counter-terrorism police are considering all possible angles, including foreign state involvement. She said the investigation is hugely complex and specialist teams are interrogating multiple lines of enquiry.

Prime Minister Andy Burnham said on Wednesday there were strong indications that Iran played a part in the incident, though he gave no further detail, and Tehran has strongly denied any involvement. US Secretary of State Marco Rubio said on Monday that the hands of a foreign actor had clearly been involved. In recent months US bombers have taken off from the base for the Middle East, after the UK approved a US request to use it for what it called defensive strikes on Iran. On Thursday the British ambassador to Iran met the country’s foreign ministry at Tehran’s request.

Why it matters

An RAF base being used for operations against Iran, with a suspect holding Iranian citizenship now arrested on suspicion of preparing terrorist acts, is a combination that puts the UK government’s account of the Fairford incident under sustained scrutiny at home and abroad. The investigation also raises the question of how a group of British nationals came to be travelling towards a live US military facility in the early hours of the morning.

What happens next

The 25-year-old dual national remains in custody while detectives continue their work, and police have not ruled out further arrests. Officers say enquiries into all lines of enquiry, including possible foreign state direction, will run for some time. Any decision on charges will be taken when the evidence supports it.