Thanks to those who have replied and I hope the replies help others in the future.

I think I had already implemented most of the advice offered as indicated in my original post. Please find the mbam log attached. At this stage it is probably only of academic interest.

I don’t believe anyone has answered my final question on maintaining confidence in Avast continuing to work correctly. It looks as if there is no alternative to regular testing with the Eicar files (http://www.avast.com/faq.php?article=AVKB32).