Thanks Mike - as indicated above, it is ,for the moment at least, sorted. No idea how or why! What this little saga has shown, yet again, that info on WiFi problems requires a depth of knowledge of 'techie speak' which I don't possess
It seems (to me) quite extraordinary that a PC function which, nowadays, is almost totally essential, continues to be presented in a form which is almost unintelligible to non-geeks, As to fault finding, as I now know, the process requires a familiarity with PC gobbledegook which exceeds anything I have gained from some 20 years of building, using and swearing at the things. Methinks there is a little fortune to be made by the first person to write an automatic check and fix program(me). .. or the manufacturer of a fool-proof system!!