system
15
Many thanks to all of you who have provided guidance in trying to resolve this CPU/RAM consumption issue so far, but sadly it still persists.
I have installed the latest version of Thunderbird and the issue is exactly the same. :o :
No other other programs on my machine, except these email clients, trigger or upset Avast in this manner.
Strange, that in all the 12 years that I have been using Avast both free and paid versions, this is the only paid version that has issues.

My next plan of action, if none of you suggest otherwise, is to completely un-install, remove all traces of Alwil/Avast from the registry, reboot several times and then install the latest FREE version of Avast.
If the problem disappears, I will kiss the money I paid for Avast Internet Security as a bad bet and stick with the free version.
.