I followed the instructions in this link:
http://www.theandroidsoul.com/nexus-...llation-guide/
Link from Whirlpool computer forum member Mark Aidan
The instructions are similar to those provided by chaley
Before following these instructions I did a system restore to before the 15th August '14 to be rid of the rogue update and set my computer to not download updates until I tell it to, so that I can un-tick the rogue one
Now calibre is working as brilliantly as before, sees my Nexus 7, lists all the eBooks I have stored on it and happily loads new eBooks
Once again all is right with the world !