17:07 UK time, Thursday, 21 April 2011
The impression is sometimes given that we are on a one-way drive towards greater openness in public life, as more and more state information is constantly being revealed.
But in fact change is not always in the same direction. Public bodies sometimes cut back transparency, deciding to keep secret material which previously they might have disclosed. One example of this is the Metropolitan Police Special Branch, the section of the force whose duties have featured monitoring political subversion and which is now part of the Met's Counter Terrorism Command.