Re: end UK dependance on GPS?
... someway that a really accurate time source provides position without the need for signals from satellites, measuring the position of astronomical objects etc.
Yes. It's called "celestial navigation," discovered (invented?) in 1837 by Thomas Hubbard Sumner. The big problem at the time was that there was no way to determine the time with sufficient accuracy when you did not know your position - thus prompting the race to invent a super-accurate clock that was impervious to both a ship's movement and temperature changes.