Update on that oddity on the BQM:
2 days ago, the computer engineer was poking around via TeamViewer and did a few bits of sorting out. I'd had two days of the system freezing up and shutting down, so they tried to isolate the problem.

It's been working fine since whatever he did, but in the process, he installed IE11 (I'd been using 9), and on the nights since, there has been no sign of any 'activity' showing on the BQM during the night when the computer is off.

Anyway, that new router is going back on Monday because the wireless was very poor, and I've bought another 7800n. Only just got it set up, so not yet sure if the wireless is working properly now.

I haven't re-read the whole thread, but you haven't got any smartphones or tablets connecting have you? Or outsiders?

I upgraded from Win 8 to 8.1 a couple of days ago. That automatically upped me from IE10 to IE11.

Last night I set up a new ASUS RT-N66U instead of the PlusNet 582n. Looking good so far.

It was a few posts back, on 26th Oct.
That new router was showing 1.2-2 hours of activity once or twice through the night, and after the IE upgrade, it stopped.

The wireless connection was secure. Sons both have iPhones, but neither were here at night, and I have a notebook but it was turned off completely.
None of them would hold the Wi-Fi connection on that router, hence it going back.

Irrelevant now though because it's back in it's box ready to go back on Monday.

The new 7800n seems OK so far! Hope your new Asus stays 'good'