Sorry, yes I did do that, thanks.
I'm hopeful that what's amiss is the WiFi connection in general, but W10's interaction with that, in particular.
Since Downloading is an order of magnitude faster than uploading (and some) I wondered if W10 (With everything in Cortana switched off) was sending stuff back to who-knows-where and in the that direction it was taking an age before the modest (12m to-me) traffic was allowed to complete.
To test it in the past, I had run the phone cable to my room and then used a short yellow lead from that. I'm not that's not a good idea so today borrowed a long yellow lead, keeping the telephone wire below a metre. I find it hard to believe that would make that much difference, but right now, hard wired, it seems to be okay after ages of being a PITA.