Three vans, masked men and a late-night tip-off: What happened outside a UK airbase?

Moments after midnight, three white vans sped along the highway from London towards the Royal Air Force's Fairford base, in England's south-west.

Before 2am, the vans parked metres from the airbase's fence line.

Watching from her home was a farmer, who witnessed multiple "hooded and masked" men bundled out of the vans and sprint into the pitch-black morning.

Moments later, police sirens filled the air.

Gloucestershire police arrested five men in the nearby village of Whelford.

Police initially arrested the men on suspicion of offences under the Explosives Act. But the charges were upgraded to suspicion of preparation of a terrorist act after counter-terrorism police took over the investigation on Sunday night.

About 85 households nearby were evacuated and relocated to a nearby leisure centre as army bomb disposal experts examined the van and established a 400m cordon around the crime scene.

The farmer who contacted police told UK media she was surprised the men got so close to the RAF base.

"I just can't process how that base was on such high alert, and that the men were even there," she said.

"I'm really glad they ran away."

What do we know about the suspects?

Police confirmed the five men are British nationals aged between 23 and 25 and all live in London.

All have since been released on bail.

Head of UK Counter Terrorism Policing, Laurence Taylor, told media on Monday afternoon that the men were released after "extensive interviews and inquiries" and were still subject to investigation.

"This does not mean the investigation is over," he said.

"They are subject to stringent conditions on their movement and contact with others."

He said the police are investigating "every possible angle" — including whether the men were "either knowingly or unknowingly working on behalf of a foreign state".

The Daily Mail and Press Association both reported on Tuesday they understood from sources that tests on materials in the back of the vans established they were "not viable explosives".

Why RAF Fairford?

Almost 150km from London, RAF Fairford opened in 1944. It was used by Allied troops for the D-Day invasion of Normandy, and by the US in the first Gulf War in 1991 and the invasion of Iraq in 2003.

In March, then prime minister Keir Starmer granted the US permission to use two UK bases to launch attacks against Iran.

RAF Fairford is one of the few European airfields that can support the launch of the US Air Force's heavy bombers.

In July, Iran's Revolutionary Guards warned the UK not to allow US bombers to fly from the base, saying it could become a target. However, the UK responded that it would be ready to protect RAF Fairford if needed.

Trump says it 'might be' linked to Iran

On Monday, US President Donald Trump said British police should not have released the suspects on bail.

"I'm surprised that they released them. I wouldn't have done that," he told reporters in the Oval Office.

"We know everything about them. We would not have released them."

He added that the incident "might be" linked to Iran.

On Sunday, Trump said the men intended to do "big damage" to the base and confirmed the group had been the subject of a long-running investigation.

"We had them under review for a long time, and we got them," he said.

He said the US and UK had been working together to investigate the incident.

UK defence minister West Streeting said the UK was "working closely" with their "American friends" and that he had been in contact with US defence secretary Pete Hegseth.

Streeting said it would be "irresponsible to speculate" if Iran was involved.

Iran embassy denied 'malicious speculations'

The Iranian embassy in London released a statement on Monday saying it "categorically rejects and strongly condemns" recent "unfounded and malicious speculations" Iran was involved in the incident at RAF Fairford.

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