I have the bellwire disconnected on my Gigaset and as I have stated above all works just fine - but who knows, might be worth a try for the OP.
But as you are connected to the master socket, then you are directly connected to the ring capacitor in the LJU
does yours still work if connected to an extension with the bell wire DIS
Good point Titanic. Unfortunately I can't test this as I don't have an extension socket - my Gigaset is a triple handset model with each connecting to the base wirelessly so I don't need any extension sockets.
Thanks all for your help. Prompted by the suggestions reagarding the bell wire being/not being connected I checked the new master socket but found there were only two incoming connections and no way to check what was coming out through the various plugged connections in the socket.
I did check the connections in my extension socket and found only 3 cores connected although one of these was orange/white which i thought was the bell wire? Anyway i connected white/orange in case I had that the wrong way around but that did not fix the problem.
However, in the process of playing around with the master socket, which is in an out of the way location, i was reminded that I had a mains powered BT REN booster unit connected in line between the master socket and the kitchen extension. I fitted this back when we had multiple corded phones and a dial-up internet connection. Not really needed now that most of our phones are cordless and the internet connection is broadband DSL so I tried taking this out of the equation....and i now have a functioning answerphone.
So I am not really any the wiser as to the cause, but my problem has gone away.
Thanks all again for your interest and suggestions which did contribute to me working through this issue successfully.