Firstly, thanks for the replies, I have read them all and thought them through. Since initially posting I have had a number of discussions, one with a professional and the others with friends.
The upshot is that I had some baggage from my military service (14Coy/ SRR) which seems to have left me with a internal sense of impostor phenomenon. Whether this is a real psychological term or not I have still yet to read up on. Is does fit with how I feel internally though, insofar as flights, before which I am nervous, should be well within my capability and probably are on paper but I don't think they are. I am told the reason that this has happened is in part because in my military career I did a very specialist role and as such my sense of self-worth was high and reinforced by the role and position. In my civilian role I no longer have this specialist role so have been left with the residue feeling of being an imposter. Not sure I understand the linkage yet.
Maintaining a high level of currency will help here I am sure as will a kick up the butt