Well, it's now being used to block access to thepiratebay and other torrent sites if I recall correctly. And of course it's now being expanded to ALL porn (though that part has an opt-out) and rape porn.
I'd call that a very clear example of mission creep.
The blocking of Newzbin was a court order, not an action taken by the Government.
It does seem that they want to regulate material 'advocating terrorism' though, which could easily be a slippery slope. Still, without evidence such an argument is fallacious.
I'd call a court order "action taken by the Government". It might not be action taken by the legislature, but it is still government mandated filtering using systems originally intended for child pornography.
I'm not sure it's really fair to say that any system which gets used by the courts is 'the Government'. Almost any system is open to abuse if it's not perfectly constructed, and the blame can lie nowhere else but 'the Government' in this case. It kinda ruins the ability to determine where the actual fault lies. Was it faulty ruling or was it badly drafted law?
I'd call that a very clear example of mission creep.