a couple of pointsthe ringing thr dialer hears is generated from the exchange not the master socket.
if there is a path to the master socket and a phone plugged in then the recievers phone rings
as i understand it there is no voltage until a call comes in which will then be about 50v
i know i have done enough phone faults and got zapped !!!!!!
everybody is talking about 2 and 5 which on extensions is correct but some master sockets have A and B for the incoming line ????
are we sure its wired correctly (sorry Matty simple question but a point to rule out)
and why do you live so far away from every one ????
if you were on my doorstep i would come and assist.
BRAINWAVE !!!!!!!!
who has an old bt master socket in their garage ???? broken or new ????
send it to Matty he can install it and test again find it faulty phone BT job done !!!!!!