After all the grief, and changing NOTHING, my speeds have been absolutely fine now for a week. So, this smells of things being messed with on the BT network and now and then causes routing problems for different users, depending on which IP they get dished out and where that then takes them route-wise.
Before I would have to re-start the HH3 every day or so to get the speeds back to 37.5 down and 8 up, having dropped to around 3-5 megs down, but around 6 megs up.
It has been suggested that I have a duff router and/or modem. But, surely after a full week of stable speeds, I guess this is not thecase.
Anyways, no complaints, all seems just OK.
Yamaha AW16G user
FujiFilm HS-10 User