UK Prime Minister Andy Burnham has said there are “strong indications” that Iran had a role in the incident at RAF Fairford over the weekend.
While Tehran’s hand has been suspected, it is the first time that it has been confirmed on the record that Iranian personnel could have played a role.
But it is still unclear whether the five men arrested were intent on carrying out a terror attack linked to the airbase used by US bombers in the Iran conflict.
Mr Burnham was asked directly by the BBC about whether the regime had a role in the incident.
“There are strong indications that Iran played a part in what happened over the weekend at RAF Fairford, but of course it remains an ongoing, complex and serious police investigation,” he said. British security chiefs are also “working closely with our colleagues in the United States of America” in the investigation, the Prime Minister added.
“We are on top of it in every possible way imaginable,” he said, adding that while he could not go into details “obviously I wouldn't say it lightly” about Iran’s involvement.
The circumstances of the incident near the airbase have grown murkier after it emerged that one of the suspects had raised the alarm with a phone call to police.
President Donald Trump and other US officials have questioned why the five men arrested were released on bail, but the Prime Minister said the “strictest possible bail conditions” had been imposed.
There are now at least five lines of investigation being followed by counter-terrorism police, from the suspects being petrol smugglers to alleged Iran proxies seeking to blow up a US airbase. Tehran has strongly denied any involvement.
While the five men from Britain, all in their 20s, arrested on Sunday outside the airbase have been released on bail, they remain under investigation.
Emergency caller
It is now understood one of the suspects called the UK’s 999 emergency service phoneline but no explanation has been given as to why.
Curiously, the call was made at least an hour before another 999 came from a farmer who had seen the vans and masked men at 1am as she returned home from a party.
Did the first caller realise he had been drawn into a terror plot? Was he attempting to panic the authorities, or even to lure police into a potential ambush? It remains unclear why armed police reacted rapidly to the farmer’s call but not, it appears, to the suspect’s.
Dry run
A key line of inquiry will be whether the suspects, who may have been part of a larger gang, were on a reconnaissance mission or “dry run” for an attack.
Mr Trump said the suspects had been “under view” by British and US authorities for some time. Therefore, it is possible that they were assessing security weaknesses and potential entry points for a planned attack on the 470-hectare site.
Petrol bombers
Were the men foot soldiers on a terrorist or criminal operation? Splinter Irish Republican Army terror groups have used incendiary devices in which detonating petrol causes a loud bang but little damage. However, this practice needs explosives to set off the device and none were apparent at Fairford.
Iran proxies
The men could have been unwitting pawns in an operation by a hostile state, most probably Iran but potentially Russia, which has been attempting sabotage bases across Europe.
Marco Rubio, the US Secretary of State, claimed foreign actors were “clearly” involved at Fairford and Washington officials raised the possibility of Iran. British police disclosed they were investigating the potential of proxies for a foreign state.
Fuel thieves
A more prosaic outcome is that, in a time of soaring fuel prices, this was a gang of fuel thieves looking to make quick profit. There are reports that the three vans were used to take on board siphoned fuel.
