Nestwatcher was the codename used by a Forge agent that monitored air traffic near the Forge Alpha Facility.
When Pegasus One, Pegasus Two, and Pegasus Three left the Alpha Facility to salvage a crashed spaceship in the Laplands, the Nestwatcher watched them from a farmhouse. Inside the farmhouse a woman tracked the helicopters with a radar. After the helicopters were out of sight, they contacted Oracle and informed it that the helicopters had left.
Later, when Charles Crichton retired, Nestwatcher that he left Dartmoor safely. This was a lie as Crichton had been assassinated by Nimrod. (PROSE: Project: Valhalla)