The AAIB report is out.
It's an 'interesting' read...
AAIB report...
After the Airspeeder Mk II failed to respond to control inputs it entered an uncontrolled climb at maximum power.
Operation of an independent kill switch had no effect and the aircraft continued to climb for 41⁄2 minutes, drifting with the wind and reaching a height of approximately 8,000 ft.
The aircraft infringed controlled airspace over a radio navigation beacon used as a holding point for Gatwick Airport.
After depletion of the batteries, the aircraft fell to the ground in a field, 40 m from occupied houses and 875 m from its launch point.
The operation of the Airspeeder Mk II during the accident flight breached conditions of the exemption granted by the CAA for the flight.