Chatham House Rules
see here:www.geocities.com/ Pacific_Future/const_chatham.html
It means a forum in which individual views can be expressed confidentially, without future attribution or risk to reputation where an individual has a "status position" as well as a personal opinion. The info aired in this forum CAN be referred to anonymously.Interesting. I'd heard the term but didn't know what it meant.
The phrase is of relatively recent origin 1980's perhaps and refers to a real place in London; Chatham House - the headquarters of the Royal Institute for International Affairs and one of the most respected of the Foreign Policy think tanks.
It's an independent research organisation which has gained a reputation as a place where the establishment can get together and exchange ideas - if necessary, under what's become known as Chatham House Rules of confidentiality.