Thank you, Essex, but I’ve done that. I am moderately computer literate, so set up the router myself originally. I now own the admin and network passwords (and they’re ‘strong’).
Is that a satisfactory answer to your suggestion?
Should I go back to the beginning and run the anti-malware applications?
Should I start a new thread?
Update.
I finally lost all Internet access again and - long story short - an independent techie found my modem had been reconfigured (no-one here even knew how to access the modem). Instead of the provider’s login and password, my wife’s e-mail address and some asterisks. He restored the appropriate entries and access was restored.
Next morning, lost access again. This time I accessed the modem and, scanning through the entries (the changes made previously stood), was intrigued (as DNS server had been one of the problems identified by Windows network diagnostics) by “Manual DNS Server” and the two IPs entered. The technician was too, and suggested replacing them with Google (8.8.8.8 and 8.8.4.4), which restored access. All hunky-dory to date - including apparently clean bank access.
I then googled with the two IP addresses, which turn out to be hosted in the Russian Republic.
That is, my modem had been reconfigured somehow to two Russian DNS Server IPs.
Go figure.
hey pingo have you tried to reset your routher witch essexboy suggested? if not please do so. second im quessing esexboy is on holyday with all right 
but if he comes online later today agian i suggest you run a fresh scan with frst+addation and attach them here so he have something new to look at.