a bit further again - after failing to regain WWW access via WiF|i I switched off the Mint laptop and went to bed, leaving the router/modem to look after itself. When I switched the laptop back on this morning everything was working properly. I don't know if the router does some sort of periodic reset or reconnect in the night but something caused the equivalent of hard reset to the router. I have previously shown that nothing I can do with the Mint laptop re-establishes the WWW access when it drops out. Ping 8.8.8.8 does not work when the WiFi has dropped the access unless a wired connection is made.
Next time it drops access I will try pinging the router,
Rans6..........................