Ben,
It may well be that your witness saw a Helicopter at that time and place but what type of Helicopter is a matter of speculation.
It is not unknown for "eyewitnesses" to convince themselves that what they saw was "the one" involved in the particular incident.
ps welcome back
W K
"The root cause of this accident is that the crew while operating in poor weather and close to high ground flew the aircraft into the ground." OC RAF ODIHAM
"The weather was suitable for the flight but would have required flight in accordance with Instrument Flight Rules in the vicinity of the Mull of Kintyre" BOI para16e
Oh - incidentally
I always understood that the Boscombe Pilots DID NOT refuse to fly the Chinook but that pre - planned maintenance was brought forward whilst awaiting further data to arrive to enable icing trials to be carried out.