Re: You are perhaps assuming that its going to be GPS in the traditional sense?
Yes, they dont have clocks.
The GPS does not need to be global for the UKs purposes. It needs to be accurate where its interests are, and last I checked, that was a few islands in the Atlantic, and perhaps the Middle East.
The Chinese nor Indian systems are not accurate outside their areas of interest - they are not global, while the satellites are covering everywhere. They make sure that enough satellites are overhead in their country at any time - they do not garentee coverage elsewhere in the world. I believe that india only plans to have 8 satellites - to cover an entire continent and 1000 miles round it.
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Actually, GPS isnt particularly useful in the far north (above 70 degrees) or south because of satellite inclination- GLONASS is the only cm accurate one there.
For the UK, satellites could be sychned from ground stations simmilar to the french DORIS system works - https://en.wikipedia.org/wiki/DORIS_(geodesy)
This can be used to calculate position data from a relay satelitte - accurate to 10 CM. The UK likely has enough ground station spread to be able to do similar with a relatively small constellation of LEO satellites.
The main issue would be the radio bands used - I dont know if existing birds could be configured to talk on the appropriate frequencies.... meaning only useful for military...
Biting the hand that feeds IT
