dt:
You mentioned not wanting to move to fibre due to not having a phone in the event of a power cut, what's your contingency for powering your cordless phones in the event of a power cut? does the base station also have a battery or something?
The panasonic phone that proved to be causing the issues has a battery back up thing in it so it will work in the event of a power cut. This new phone I have just got out of storage and got working again also has a battery back up thing in the base and will work if the power goes out. AND I have an old corded phone that plugs directly into the jack point that obviously will work. There is not enough cell phone coverage at my house to be able to make phone call using a cell phone.