Who Owns The Maunsell "Sea Forts"?

See last photo:http://www.boston.com/bigpicture/2009/04/human_landscapes_from_above.html
I saw these things mentioned years ago, when “pirate” radio stations operated from them…who owns them now?

The Royal Navy owns a few, with the British Army owning the rest, near as I can figure. When some of them needed to be dismantled a few years back, they sent in the Sappers.