Excuse me for not having a real answer. Only in the margin:
On the general trend, NDB's are a thing of the past. In Europe at least, and probably elsewhere too, they are being phased out quite rapidly.
The UK is of course a somewhat peculiar place - by which I mean nothing negative! - but sooner or later the NDB's will be going there, too. Fazit: even if some remain today, don't count on them being there tomorrow. The future is all for SatNav (called "GPS" by some) which is cheaper both for operators and for users, and more accurate.