Those of you who are advocating taking a proven US product and refitting elements of it with UK kit are fooling yourselves.
1. Why do it when what is already there works?
2. Anyone who knows a bit of aviation history knows that when we do this the outcome is a) More expensive, b) less capable, c) late.
Phantoms anybody?
Also, in the case of the P-8, the Mission system is not a system in isolation. It interacts with the "standard" 737 - type flight system. Another integration issue to cause problems when trying to introduce a non-Boeing mission system to a Boeing flight system.