Technically can you identify the source of a call?

[#1]

Why would you?  Well, because plenty of people get silent calls or fraudulent calls which are recognised as such and dialling 1471 tells us that "We do not have the caller's number." 
So if IMMEDIATELY I call PN to report above call and it is the very last one received just a moment ago can you identify its origin?  Can this number then be watched and 'blacklisted'?
Maybe I can spot most  / some frauds, but others may not.  A blacklisted source would save lots of anguish.

[#2]

It can be done - but only at the Service Provider level.  In the Plusnet case this is BT.    Not normally done as a User service, but can be invoked for malicious calls investigation.
It is a User option to not display their No.    BUT!  It is a mandatory component of the signalling protocol managed by the Service Provider.
Maurice

[#3]

We're not really able to trace individual calls in terms of geography I'm afraid. If you are getting bothered by unsolicited calls I strongly advise registering with TPS (telephone preference service).
http://www.mpsonline.org.uk/tps/