Can't really see much chance of the cruise boats being used as auxiliary transport should the need arise, seeing as how Cunard is now US owned. I don't think that there's a UK based cruise fleet with the fashion for flags of convenience in the late '80s and '90s to cut costs & allow for cheap crews.
Can't honestly see the need for all this posturing and sabre rattling in any case, but then again, that would need politicians to stop squabbling, act like adults and admit that there might be some problems that their particular policies either can't fix or are the root cause.
