Re: end UK dependance on GPS?
You don't need a local accurate clock: with 3 satellites you do, but with 4 you can solve for position and time. All that this would do is eliminate the need for one degree of the solution, but you really want more than the minimum anyway because (a) some might close together leading to the "geometric dilution of precision" and poorer fix accuracy and (b) with N+1 you can tell if one satellite is flaky, and with N+2 you can tell which one it is.
So really all that you get from an accurate local clock is a benefit if you are using GPS for time sync (important for mobile phones, DTV, etc) as you can run for longer between synchronisation times. What you don't get is navigation without some form of triangulation (even if star tracking...)