Gary, generally, the 999 network is answered by local centres, however, when the demand is huge a 999 call from say, southampton, may be answerred by someone in manchester.......unlikely, but possible.
The 112 network is picked up by centres local to the origin of the call. Also, when calling from a mobile phone, the general location of the caller can be determined by using trignometry if the ignal is picked up by three or more masts. This is how n'ere do wells may be tracked using big brother technology. It falls flat when only one mast picks up the signal, so the calculation cant be made. One good thing about the mobile 112 system, is that calls made are directed to the closest network, not necesarily your own network, so, say a call from an orange mobile can be picked up by an o2 mast, etc etc, even when your own handset signal is poor. Remember the guy who was located in a remote part of the world by calling his family back home??? It does work, alledgedly.
Rich