A farmer driving home from a party near RAF Fairford spotted three suspicious white vans blocking a country road and masked men in balaclavas scattering into fields toward the US air base, then turned around, called police and warned residents to lock their doors. Armed officers arrested five men on suspicion of preparing a terrorist act within 25 minutes of her call, The Telegraph reports. The men had first been held on Explosives Act offences after police received the report of three vehicles heading toward the base at 12:45 a.m. on Sunday.

An Army bomb disposal unit is examining the vehicles, which sat roughly 350 meters from the base perimeter inside a 400 meter cordon, and about 85 households in Whelford have been advised to evacuate. One van carried fake Fuel2You branding and a phone number that went nowhere when dialed, and the fuel delivery firm whose livery it mimicked said its vans had not moved. RAF Fairford had raised its force protection level to Delta, the highest US level, hours before the call, and the highest alert levels are now in force at British bases hosting American forces, with Lakenheath at Charlie, indicating authorities anticipated a threat before the farmer raised the alarm.

Counter-terrorism police are leading the investigation. Investigators view an Iran-linked motive as the most likely explanation for the plot, and sources familiar with the inquiry believe Iranian operatives were directly involved rather than working through proxies, The Telegraph reports. Fairford is the only base in Europe where the US keeps heavy bombers ready to fly and has hosted B-1 and B-52 missions against Iran this year, and Iran's Revolutionary Guard has previously named the base a legitimate target, though police have not confirmed any connection between the arrests and that threat.