I'm still of the opinion that a contributory cause was the lack of radar cover at low level in the area.
Macrihanish radar had been withdrawn about 2 months previously; the crew would know this and rather than fly IMC without radar above safety altitude in an area where there might be other traffic doing the same thing, they elected to stay VMC below. Of course the official inquiry would cover up this fact to cover their superiors from any blame (as far as I can recall, RAF Macrihanish still operated, it was just the radar that had been terminated, probably to re-site it elsewhere).