ShotOne:-
I just don't buy the line that we face a binary choice between a tortuous modification process and having something designed and built from scratch
I'm not sure that anyone is suggesting that, are they? The Hercules CMk1 was a good example of an RAF "Bespoke" aircraft. A bog standard Airframe and Engine package (though we wanted to hang Tynes on them!) was packed full of UK Avionics (not very successfully, though that's another story). It was also a very good example of us knowing better than the lead operator, the USAF, who specified ESF and FiiS for the fuel system. We didn't, and had to replank the wings and later retrofit ESF after 10 men had died. As I say, it is not COTS that is the problem but the MOD...