“There are certainly those who would call this an ambush patent”

UK MoD Attempting to Coop American Ingenuity That Brought GPS to The World? 
And the rest of the world might get to pay MORE for GPS equipment and use of the system because of it.

I'd call this worse than 'ambush patent' activity.  I call it bureaucratic rent-seeking parasitism at it's Euro-finest. I would also call it a form of 'Lawfare'.

GPS III Upgrade: To Include Paying the UK for the privilege of using our own systems?

One solution: charge any b*stards who charge us the equivalent for whatever part of the GPS system that up until this point has been 'free'. Make it retroactive.