What I suspect is an ancient document on the WWW says:
<< All test equipment used within NATS is accepted, repaired and
calibrated at RMS at Pailton, near Rugby. Its responsibilities include monitoring
field strength and frequency of navigational aids and aircraft telecommunications, the standards for radio and electrical measurements, and the management of test equipment throughout the organisation in liaison with CTO (CSM), to whom RMS reports.>>
Whether that is still true I do not know. I do know that donkeys years ago it was listed in the COM section of the Air Pilot as "Pailton Radio Measuring Station" and a frequency was published for aircraft to use for radio testing. I'm not aware that it is either part of the multicarrier network, or houses any nav aid(s).
I accept what eglnyt says about the "cone of silence" but I think you'll find that the vast majority of radio nav-aids are centred under airways or under the holding patterns which they serve.