Please feel free to read the CAA's regular incident report publications.
You can then check with various other countries safety data units to get the numbers.
To look at it from a practical point of view - NATS has to pay to keep the 121.50 autotriangulation service operated by D+D and one of the reasons for it's use is the high number of airspace infringements in the SE region (this is where the coverage is the best). This charge is passed on in route charges.
No other country requires ATS providers to spend that money becuse they have the same level of safety without it. Yes they have DF and other facilities to assist pilots in emergency. But ask any other authority if there is a need to provide any extra service for pilots who reguluarly get lost and the answer will be no.
Ask any other country if given the choice, would they provide better VDF autotriangulation coverage over flat well populated areas with numerous landing sites and lots of ATS units with good R/T and radar coverage or over sparsely populated areas where the terrain is difficult, the radar coverage is poor and search + rescue difficult.
Again I ask - if other countries can cope very well without it, and other countries do not have the same number of lost pilots, what is lacking in the UK that makes it necessary?
I believe that the availability of autotriangulation is an asset for flights in a state of emergency (mayday) or urgency (pan). I also believe that with nothing else to do, D+D should note any callsigns of non-emergency transmissions on 121.5 and report them to the CAA for further action.
Why spend money on a VOR/DME or even a GPS when one can call 121.50 every so often and let them do the work of fixing your position? After all, they welcome the practice don't they?
Regards,
DFC