Gness had the same problem as I did-- crackly phones. I hope he/she might see this. My son-in-law came round. He seems to know a lot about phones and he has some test equipment. He found there was a break in the line between two sockets. The cables run on the outside of the house and one of them is not meant for outdoor use. The cable has four wires and only two are needed, so he was able to use the other two wires which did not have breaks in them. Obviously, this 'repair' will not last for ever, but we'll know what's wrong when it happens again, and we'll be able to replace the cable (I hope).
Bert...thank you very much....when my clever friend or brother visits I will get them to look at this....it may be my answer and wouldn't surprise me when I remember what other bits were like when I moved in.
I have had everything inside the house checked....so this looks like my next step.