I think we're getting a bit deep here. Weekends excepted, the vast majority of the country has radar coverage to some degree. You've just got to select the right unit, and it doesn't matter whether or not it's a published "LARS" unit - the same services are available from all, although of course their primary task takes priority.
Weekends are a bit trickier with most military bases closed.
The cost of upgrading an airfield to a radar unit is astronomical. Not just the cost of the equipment, but surveying, flightchecking, design of new approaches, re-writing the airfield manual, training of new controllers etc etc. If you haven't got the commercial back-up, it's not going to happen.
What may become more prevalent, however, is the remote siting of a radar unit, as for instance at Finningley. The radar there is done from Liverpool. The commercial case there though is that both airfields are Peel Holdings so the ATCOs work for one company, and airlines pay!
The drawback, however, is that the radar controllers have no local knowledge.
ap