@Steve - I think you are referring to the HRA and ruling that Housing Association is a public body in the eyes of that piece of legislation. FoIA is very clear on what a public authority is and isn't. Because a determination is made under one Act doesn't mean it applies to all Acts. Course the ICO may say they expect a HA to act within a piece of legisation.
Personally l think FoIA is a clunky nasty piece of legislation which doesn't achieve the spirit in which it was designed. I think better to encourage openness and transparacy rather than legislate.