@David-TP I appreciate your suggestions, however, I don't have this device any more, as I've returned it to the retailer after about a week of trying all sorts of tips. It was originally purchased on the 12th of this month.

But if you can guarantee me that we can either get one of these Archers going consistently better than say 150 megabits / second (my router's max is 300 in theory I think) or I can get a refund, then I would be prepared to purchase another (even directly from TP-Link online shop) and try again, because it looked like a well made unit, and it's probably just a Windows update which has caused these problems. (Many people seem to have problems with Windows 10 and various USB wifi adapters based on Realtek chip sets, as far as I've discovered over the last week or so.)

Thanks again,

Roger V.