We have not solved the problem and I now know that a neighbour has similar issues. I am no longer having disconnects though. Although it's not possible to pinpoint the external interference, that's undoubtedly what it is.
I have closed the ticket after what I can only describe as first class service. I ended the question conversation with this:-
"Thanks for the call and my apologies for not updating this yesterday.
I'm not sure the problem has been resolved but the connection has stabilised just as it has done in the past with no action by me or PN.
<snip>
Thanks for your excellent service.
I will now close the ticket via your latest email."
