OK, a couple of things....
It wasn't possible to uninstall Avast via control panel, but I thought that was the whole point of the download and safe mode technique? Anyway, I followed that and it appeared to work.
When reinstalling Avast I got the same 'blocked by group policy' message before it finished, but then it did finishe and it said it installed....
I ran the scan as directed and only one text box came up and was saved....as follows: