Amazon is spotted testing its Prime Air delivery drones at the company's test site near Cambridge

Amazon is continuing to'secretly' test the capability of its Air Prime delivery drones at their proving ground in the UK countryside. Engineers in high vis jackets were spotted yesterday flying drones on wires from a giant metal gantry in a field near Cambridge, England. It is unclear why the drones are being flown attached to cables -- but could perhaps help to determine the drone's positions relative to the crane as they land. Cameras and sensors have also been added to the metal frame to carry out tests on the drones and check they can navigate and land correctly. The company first began secretly flying its drones in a field near Cambridge three years ago, in July 2016, after the UK's Civil Aviation Authority lifted the previous strict drone flying restrictions.