An investigation into why four men were killed in a horror mid-air crash last week could take up to a year, it has been revealed.

The Air Accidents Investigation Branch (AAIB) told the Bucks Free Press the debris of the helicopter and light aircraft had been moved from the crash site in Upper Winchenden to its headquarters in Farnborough to be looked at in more depth to try and determine the cause of the incident.

The aircraft collided mid-air near Waddesdon just after midday on Friday (November 17).

AAIB spokesman James Hopson said these types of investigations can "typically" take up to a year to reach a conclusion, adding that detectives would be looking at the electronics of both aircraft, including black boxes, and also the radar from the area.

He also said the black boxes from the aircraft were not likely to be as sophisticated as ones found in commercial airlines.

It comes as more pictures of the wreckage at the scene have emerged.