I wonder if in this day and age a 500-year old book like "Vindiciae contra tyrannos" (http://en.wikipedia.org/wiki/Vindiciae_contra_tyrannos) would land his/her author in jail. I suppose it would. And I cannot remember the exact title, but there were books similar with this one, written at about the same time, which were advocating for even more drastic measures: i.e. the assassination of the tyrant/king.
Anyway, in the US it has been illegal for some time to say "I want to kill the President of the United States of America" (https://www.youtube.com/watch?v=QEQOvyGbBtY), the UK had remained one of the few countries where a liberty of speech "loophole" was still in place. Sad to see it gone.