Nicholas,
Thanks for your reply.
If I were an FO I think I would make sure I knew from my employer what the legal position was before I started out. I would want to know what I would be legally permitted to do in the scenario I paint. I would want to know that I would not be prosecuted for taking command from the designated commander In the event of my being without employer guidance in advance and facing prosecution I would not know what else to argue in defence ( any ideas?- are you a pilot?) Notwithstanding any legal advice after the event , I would have acted at the time with the public interest defence in mind
In another sphere say,facing discosure of sensitive information for which there is no statutory gateway but with a belief that it was necessary to disclose to prevent a ( for example) crime, I would invoke the same defence. Indeed, the advent of the Public Interest Immunity Act arose subsequent to the Clive Ponting ( MOD) prosection wherein the Judge instructed the Jury that there was no public interest defence in disclosing sensitive information. The Jury very properly ( imho) ignored the ruling and acquitted Ponting etc.
Best wishes and Season's greetings