Firstly apologies for posting in the incorrect forum, and thank you for the responses. I'm humbled by the detailed and thought provoking discussion. Thanks again.
In response to some of the points made.
Unfortunately I don't have another router to try, and indeed I don't currently have physical access to it as I'm in Greece for a few weeks. But I do have access via a VPN (when the line is up) and now have other observations. Since the original post, I've been monitoring noise figures and gain and these do not change! This suggests to me that the router is not measuring these, rather are just reporting some default values. The only parameters that change are the upstream and downstream rates which fluctuate at just under 10 and 40 Mbits / sec which is what I would expect?
If it is the battery issue as discussed above, and this seems very plausible, then I suspect I'll have an interesting conversation with TT telling them to task OR to investigate unless someone can tell me otherwise.
For info, we live in a residential area of Weymouth.
However, I've noticed something else, after a reconnection, the router reports a connection up time of x mins (say) but also reports a system up time of about x mins, suggesting that the router itself has been off, I would assume that in the event of loosing its connection, the router would stay active (is this a valid assumption?) if so, it might be the router? But why would it go off every 7 OS so hours for 70ish mins? That said, based on the noise etc comments above, I probably have reservations about these time up parameters.
Attached to the router is a nas (which provides the VPN into my home network and a raspberry pi based Web server plus a few other non wired devices, now I accept that my next question is probably out of scope for this forum, but could something attached be causing this odd behaviour?
Once again thank you all for your thoughts.
Paul