In the early hours of Sunday morning, a resident of the village of Whelford was driving home when she saw three white vans parked on a country road.

She was immediately suspicious, she said – all the more so when she spotted a “large group of hooded and balaclava’d” men.

She called 999 – and police arrived on the scene 15 minutes later.

The resident, who asked not to be named, told the Press Association: “It would appear that by doing so I just derailed whatever they were planning. A plucky amateur shouldn’t be spotting an unusual bit of activity at 1am when the airbase is on high alert. I think it’s absolutely astonishing.”

If there had been no 999 call, it appears the authorities would have been unaware of the vans, and the potential threat they posed to nearby RAF Fairford.

People living in the area have been used to disturbance from protesters and a heavy police presence ever since the decision to allow the US air force to use it as a base for attacks on Iran.

But in recent weeks, they have noticed dramatically increased security measures, with the gates of the base newly barricaded.

“In the prior few weeks they have put heavy, very heavy vehicles across all gates,” another resident said.

She described them as “very big tractors and things like that” parked behind gates into the base, adding: “So obviously they’re taking security seriously.”

The resident said “great big concrete walls” had also been placed behind some gates, including on Dunfield Loop and Whelford Road.

If local people had questioned the necessity of those steps, they may have been persuaded this weekend. In the early hours of Sunday morning, others in Whelford noticed became aware of suspicious activity as the local WhatsApp group lit up with messages.

One resident of Whelford, named Jason, who declined to give his surname, said they were first aware something was happening overnight at about 1.30am, when people on the chat group started discussing the vans.

Julian Tudsbery, who has lived in Whelford for 30 years, said that the 999 call had only come after an attempt to contact the airbase itself. “Evidently, they phoned the airbase police, who didn’t answer the phone,” he said. “It just rang out, so she dialled 999.”

A photograph published by the Daily Mail showed police arresting five shirtless men at night. Police later confirmed that five men had been taken into custody on suspicion of explosives and terror-related offences.

Residents were then woken at 6am by police banging on their doors and telling them to leave immediately. People from 85 households were taken to a nearby leisure centre.

Tudsbery added: “[The police] were then banging on the door, so I went downstairs in my dressing gown.There were several police, three police cars in the drive, and they said you need to evacuate, there’s been a major incident, said he couldn’t elaborate.”

Thirty emergency vehicles were seen in the village, with the army, a bomb squad and counter-terrorism police all investigating at the scene. Explosives experts were seen examining the three vans.

The RAF base has come to prominence since March, and the beginning of the US-Israeli war with Iran. From the perimeter of the RAF base it has been possible to see heavy bombs being loaded on to American aircraft.

Fairford has a particularly long runway, which extends almost 2 miles (3km). It is reinforced to support heavy bombers such as the B-1 and B-52, which have been deployed in attacks on Iran. The aircraft are capable of carrying large payloads, including “bunker buster” bombs.

Jason, 50, was evacuated to Cirencester leisure centre at 6am on Sunday with his family and 11-week-old puppy, Poppy, and friends who were visiting from London.

“We went to bed,” he said. “It was early the next morning when the doorbell rang. It was the police, asking residents to evacuate as there had been a major incident.”

Jason, who works in consulting, said earlier on Sunday there were about 40 to 50 people in the leisure centre, ranging from toddlers to elderly villagers, as well as a number of dogs. He said they had been given no more details than those that had been released publicly by police.

The Fairford youth football club, about 1.5 miles north-west of Whelford, was taken over as a temporary base for the emergency service response to the incident. There were several police vehicles, ambulances, fire engines, pop-up tents and a large mobile command-unit vehicle in the grounds.

It was unclear when people would be able to go back to their normal lives; those at the leisure centre said they had been asked by authorities if they had anywhere else to stay on Sunday night.

By Sunday afternoon, the cordon around the village had expanded so no one could get anywhere near it. Access to the village of Whelford remained closed. With RAF Fairford located along one side of the road, a single police vehicle acted as a blockade against further passage into the village.

Tudsbery said he hoped he could get home soon: he had left his cat, Misty, behind.