Thanks Ty and others...
Seems I made a shocking mistake - unforgivable really.
I had exactly the same holding page on all my city sites. There was nothing different on them - identical title, description, page content, and Google dumped them in all one fell swoop.
Ty can vouch - there was absolutely nothing showing up in Google at all for some of them - absolutely terrifying!
Now there is a revised holding page on them, Google seems to be slowly bringing them back from the wilderness (phew!)
SEO is the next thing to look into... think I'll start a new thread asking for advice on that!