found the aaib report online here is the conclusion:
Conclusion
The cause of the accident was not positively determined. Although no technical reason was found to explain it, a technical fault, whilst considered unlikely, could not be ruled out entirely. The available evidence indicated that the helicopter was intact when it struck the trees and that the engine was delivering power. The aircraft’s trajectory suggested that the pilot was in control of the aircraft at the time of impact and was attempting to recover from a significant deviation from his intended flight path when the helicopter struck the trees.
The descent into the Mouse Water Valley appears to have been a deliberate manoeuvre. Considering the video evidence, the pilot’s intention was probably to fly a hard, right turn at low height within the valley, possibly leading to a further, final zoom climb before landing at the helipad. A high-speed, low-level turning manoeuvre in the heavily wooded valley was a demanding one, which would have subjected the helicopter and its occupants to an increased risk. The circumstances of the accident, which included a strong tailwind, suggest that the pilot needed to fly an unexpectedly high performance manoeuvre which led to, or contributed to, the flight path deviation. This deviation may have been due to a servo transparency encounter, spatial disorientation, misjudgement or some other factor or combination of factors.
