Yes, it's more than a little irritating. Thank you for your advice, I will look into Revo. I'm not expecting to need it to remove CCleaner, but I guess it would work there too.
It's ironic, I have been a CCleaner fan for some years and was on the point of upgrading to a paid version, but that isn't going to happen now. Software companies operating in the security area just don't seem to understand how important trust is. Installing software without express permission and then being unable to provide utilities to remove it properly, show of a lack of professionalism combined with incompetence. So it's goodbye CCleaner and Avast, I wish them all the success they deserve.