In a statement, Counter Terrorism Policing said the man was arrested in Westminster, London, on suspicion of preparing terrorist acts under Section 5 of the Terrorism Act 2006.

“ A 25-year-old man, a dual UK/Iranian national, was arrested in the Borough of Westminster, London, on suspicion of preparation of terrorist acts under Section 5 of the Terrorism Act 2006,” the police said.

Searches of two properties were also carried out in the area.

Senior National Coordinator for Counter Terrorism Policing Vicki Evans said the investigation into the events in Gloucestershire was “hugely complex”, with specialist teams pursuing multiple lines of inquiry.

“As we’ve made clear, we’re looking at all possible angles – including possible foreign state involvement. I’d like to thank the public for their continued support and patience whilst we work through this investigation,” Evans said.

Five men in their 20s, who were arrested on September 27, remain on police bail after being detained on suspicion of preparing a terrorist act and committing explosive offences.

The men were arrested after three vehicles were found travelling towards RAF Fairford in Gloucestershire. They were later released on bail.

The BBC reported that one of the men had called 999 himself about an hour before a local farmer alerted police to a “large group” of masked men near the vehicles.

Police had earlier declared a major incident following the discovery, while dozens of homes near RAF Fairford were evacuated as a precaution.

Police later told the BBC that a quantity of petrol was found during searches of vans near the site, but no explosive devices were discovered.

UK Prime Minister Andy Burnham said on Wednesday that there were “strong indications” Iran had played a part in the incident, the BBC reported. He did not provide details supporting the claim.

Counter Terrorism Policing said it was examining all possible lines of inquiry, including potential foreign state involvement.

RAF Fairford has been used by US military aircraft, including bombers, which have reportedly deployed from the airbase to the Middle East in recent months. The UK previously approved a US request to use RAF Fairford for what it described as defensive strikes against Iran amid the ongoing conflict.