‘If liberty means anything at all it means the right to tell people what they do not want to hear,’ wrote George Orwell in his preface to Animal Farm.

It is a line that has gone down as one of the great capsule defences of dissent, made all the more prescient by the fact that the preface, an attack on the self-censorship of the British media during the second world war, wasn’t published until the 1970s.