Re: end UK dependance on GPS?
I'm afraid you explanation is incorrect. A 3d fix needs 4 satellites as you need to solve for time and 3 spacial variables, which is why GPS receivers can typically provide very accurate time output, as they already solve for that.
The time/frequency references used for static telecoms start with a survey mode which removes 3 variables, and then allows you to get pretty accurate time with just one satellite (the ephemerides and an L2 receiver can give you a lot of ionospheric compensation).
Portable atomic clocks are great tech, but won't really help with GPS as even if you ignore relativistic drifts, you'd still need 3 sats for a 3d fix.