The Standards Board for England has published guidance on what is confidential for local councillors and the like, which is clear and succinct; other people may find it useful. It says:

Information is confidential:

* if it is about something serious and not trivial
* if the nature of the information is sensitive or personal, for example it is a business secret
* if it is information that you would expect people would want to be private
* if it was divulged in a way which implied it should be kept confidential
* if disclosing the information would be detrimental to the person who wishes to keep it confidential.

The good thing about this formulation is the emphasis on thinking what the person (a normal reasonable person) would want, and thinking about what they implied rather than specifically stated. Not news, but it sets it out well.

The full guidance on the web: http://www.standardsforengland.gov.uk/Guidance/TheCodeofConduct/Guidance/Quickguides/DisclosingConfidentialInformation/

The Standards Board sets standards for how local councillors and other elected/quango people should behave and investigates complaints: on the web: http://www.standardsforengland.gov.uk/

Their links site gives links to the Boards for the other countries: http://www.standardsforengland.gov.uk/aboutus/Usefullinks/