Remind us all what the icing clearance was for the Mk.2 Chinook at the time.
We're at risk of going over very old and long-tread ground here, but apart from the lack of an icing clearance, the aircraft type didn't even have a valid release to service. The MOD (test pilot) department responsible for producing it had refused to fly their example of the type, out of general safety concerns. The "Mull" pilots could possibly have been Court Martialled if they had refused to fly the sortie as ordered on the day; they would have been fully aware of this fact because as far as the military were concerned it was an operational theatre, albeit not publicised as such for political reasons.
At least civilian pilots don't have that pressure put on them from above, but they could lose their job over a refusal to fly, especially if the man paying your salary is your passenger. Disregarding that, there is always a personal desire to get the job done whatever, but as I've said here before, it can be a very fine line to tread.