Having read all the posts in this thread I want to give my professional opinion as an ex-D&D controller at the Scottish ATCC.
Firstly there has been debate as to whether the Captain should or should not have called a mayday and whether he'll be held accountable;
There are two states of emergency (see CAA document CAP413 here
http://www.caa.co.uk/docs/33/CAP413.pdf)
Distress A condition of being threatened by serious and/or imminent danger and of requiring immediate assistance, for which the RT call is Mayday. and
Urgency A condition concerning the safety of an aircraft or other vehicle, or of some other person on board or within sight, but does not require immediate assistance, the RT call is Pan.
There are posts in here from people who have spoken directly to the crew and there is doubt that the pilot felt in need of immediate assistance. So which distress call to make was a no-brainer, it had to be a Mayday (I don't see the relevance of a comment posted in here about a police superindent thinking it was unusual, this is outside of his professional competence).
I cannot envisage, given the circumstances described, that there will be any 'blame' attaching to the captain for over reaction (if indeed hindsight shows that it was an over reaction). Every controller that I know would much rather pilots reported emergencies accurately. Yes it is no problem to upgrade a pan to a mayday, but by the same token it is easy to downgrade. If you come in with a cautious pan, because you fear the repercussions of a mayday, then it is possible that it may work against you. The time interval between pan then mayday could be wasted because that time can be used to launch the rescue choppers and get them heading toward you. No-one in ATC would
EVER castigate a pilot for declaring an emergency.
Secondly; Kinloss is mentioned because thats where the Air Rescue Coordination Centre is based (there are no rescue choppers there, although some are along the coast at Lossiemouth). The choppers are scrambled almost by routine, irrespective of the location of the aircraft in distress, because in the event of a catastrophe in addition to rescue they will be used to ferry the injured to hospital. There is a whole rescue organisation equipped, trained, willing and in fact just waiting around to come to your aid when you feel you need them.
Thirdly; In my professional opinion (irrespective of the opposing views posted in this thread about what actually happened on board) the captain reacted in an exemplary and professional manner to an undoubted threat to his aircraft and its occupants (whether real or perceived) and is to be congratulated.
Altercations on an aircraft in flight cannot be resolved whilst still in the air because the captain has an aircraft which has to be flown. They can be debated safely on the ground. When all is said and done what was lost by the aircraft diverting? Everyone got home in one piece and that may not have been the case otherwise.