Thank you! That indeed may be "very simplistic", but most of that I did not know.
However, progress has now been made.
The incoming land line is run to my desk, where the ADSL filter, router and existing 'phone (and computer) are located - as below . . . .
Incoming line ▬ OR Master Socket type 5C ▬
cable to ADSL filter: O/P 1 = feed to 'phone; O/P 2 = feed to router.
When I plugged this phone-under-test into the 'phone O/P of the ADSL filter, I could dial out and receive calls, but no other functions on the 'phone worked.
However, when I plugged this 'phone into the OR Master Socket instead, things came to life. An investigation has revealed that the
cable from the OR Master Socket to the ADSL filter is a
twisted pair only. Thus there is no line voltage to the 'phone when it is plugged into that ADSL filter.
So it seems to me that if I wish to use this 'phone on my desk, that cable will need to be replaced by a four (or six)-wire cable, or re-locate the ADSL filter to the Master Socket and then run separate cables from it to the router and the 'phone: doing either will not be difficult; the first option will be the easiest.
If there are any misunderstandings in all of that, I'd appreciate being told accordingly: thanks.
Al.