Yes, it is compulsory. I don't know what it is like now (it only appeared in my last year of school so I wouldn't be surprised if it had been refined since then), but it used to be the case that nobody could really be bothered and within a few months, nobody in the school was doing any of the work they were meant to. That was probably due to how it was presented: they had these daft booklets which were basically "fill in the blanks" with your opinions on various moral and work related issues. There wasn't a whole lot about the political system as such, it was more an extension of the compulsory GCSE RE syllabus trying to get people to form opinions.