Well it seems as though I'm going to have to buy a new hat and eat it!
I uninstalled COMODO and hey presto the avast permissions issue disappears. That is a little off seeing as Avast! seemed to function perfectly well for months (along side COMODO) without any issues arising. Anyway I've ditched COMODO and replaced it with Outpost Pro (which I used to use).
As I said before I don't use Windows Defender, in fact I've been a bit slack when it comes to on-access spyware/malware protection simply because I am not aware of a reliable, non-memory hog anti-malware programme (that also happens to be free ware). I was also unsure as to whether Avast! could countenance another on-access scanner in its midst (hence Windows Defender is off). I would appreciate suggestions for good anti-spyware, anti-malware and anti-trojan freeware (please don't suggest AVG I had a bad experience with them a while back; they beat me and locked me in a cupboard.
).
I remember a time (perhaps through sheer ignorance) that anti-virus scanners where advertised as a catch all. Now it seems that one needs separate on-access scanners for spyware, malware, greyware, trojans and alike (the latter being very difficult to come by). Surely these all come under the same blanket term (virus)? Or is that me being naive?
Anyhow I must dash now, I have a hectic commute ahead of me. Thanks for all the assistance DavidR, much appreciated.