How did a farmer foil suspected terror plot near UK air base?

A farmer driving home in Gloucestershire at 1.30 am spotted three abandoned vans blocking a road near RAF Fairford, which the US uses, and saw masked men fleeing. She called 999, leading police to arrest five men within 25 minutes. Police later evacuated 85 homes and examined vans. The suspects are being held on suspicion of preparing a terrorist act.