More for anyone else finding this thread than anything else:
Well – after literally two hours of scrolling back through the support forum (seriously dudes, fix the forum search issue, then maybe you’d get fewer help requests!) I find this:
The gist of which is that it’s nothing to do with plugins, etc – it’s to do with a corrupted database. In my case I think this was caused by installing and deactivating plugins, I can’t think that I did anything other than that, so I would suggest it should be a bug, but not sure whether to add it to Tracker. Any thoughts?