BBC News - Paul Clifton
Imagine a corridor in the sky that stretches between Reading and Coventry.
You cannot see it but some of it is there already - a 6.2-mile (10km) wide route for pilotless drones.
It relies on a line of beacons on the ground, which communicate with the drones to make sure they are kept apart.
Testing is under way, with around one third of the beacons already in place and the rest due to be built by May 2024.
The drones will stay below 328ft (100m) altitude, out of the way of larger aircraft.