Five men were arrested on suspicion of explosive and terrorism offences after armed police stopped three vans travelling towards RAF Fairford.
The group, detained in the nearby Gloucestershire village of Whelford, in the early hours of Sunday, were "looking to do big damage", US President Donald Trump said.
The police operation was not intelligence-led, meaning investigators had not known about any potential plot in advance, the Press Association understands.
A resident called authorities after seeing the vehicles "blocking the road" before seeing a "large group of hooded and 'balaclava'd' men".
The Whelford resident told PA "they would have seen the bright headlights" and "they probably thought we were the police (and) panicked".
Officers arrived about 15 minutes after she raised the alarm, she said.
Residents had at the time understood the base was on lockdown because of a terrorism threat, the woman said.
"A plucky amateur shouldn't be spotting an unusual bit of activity at 1am when the air base is on high alert," she told PA.
"I think it's absolutely astonishing."
Gloucestershire Constabulary said it received reports of the suspicious vehicles travelling to the base about 1am on Sunday.
Officers arrested the men under the Explosives Act and they were later further arrested under suspicion of preparation of a terrorist act.
Aerial footage showed a bomb disposal robot spending hours inspecting three white vans, two of which had open rear doors.
Large black barrels appeared to be scattered around.
A 400-metre cordon was erected and 85 evacuated households were unable to return home overnight.
The army's ordnance disposal unit was still examining the vehicles in the cordon by the evening, Temporary Chief Constable Maggie Blyth, from Bedfordshire Constabulary, told reporters.
Agencies "believe the matter to be contained", she later said.
Prime Minister Andy Burnham said the incident was "deeply concerning" and the government would "always take every step necessary" to protect people.
The arrests come amid heightened concerns around the threat from hostile states to the UK, with Russia and Iran among those that have used proxies to commit crimes on their behalf on British soil.
In March, officials said the number of national security cases involving activity by hostile states including Iran increased 50 per cent in the six months to December 2025.
That same month, after then prime minister Keir Starmer granted permission for "defensive" US action against Iranian missile sites from UK bases, four American bombers landed at RAF Fairford and the US started using British bases for "specific defensive operations".
Separately, a spate of anti-Semitic attacks on Jewish sites in London in 2026 were claimed by a group called Harakat Ashab al-Yamin al-Islamia, the Islamic Movement of the Companions of the Right (Hayi), which is thought to be backed by Iran.
Support for Iran's Islamic Revolutionary Guard Corps and Hayi was banned in July by Starmer.
Defence minister Wes Streeting told BBC News on Monday that he would not speculate about motives of a live investigation.
But he said on the general Iranian threat to the country: "We know that Iran and their proxies wish to do us harm. We know that they hate our democracy, and we know that we regularly have to thwart Iranian attempts to threaten either our interests or indeed our allies."
Trump praised the UK response and suggested authorities already had the suspects under investigation, despite others' claims to the contrary.
"They were looking to do big damage to our fort, and working with the British worked out great," he told reporters in the US.
"We had them under view for a long time, and we got them. Thank you."
with Reuters
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