Crass were all about anarchy. They were highly influenced by the Sex Pistols at first, but later grew to hate the Pistols bitterly; calling them sellouts and phonies.
They formed in 1977 and broke up in 1984. Over that period of time they preached and published anarchistic ideals, newsletters promoting social upheavel, and songs damning the British Government.
For a detailed history of Crass, click here