Is it a criminal offense to tweet "kill all white men"?

This distinction used to be well understood in English common law. To be guilty of incitement you had to, you know, incite someone. In other words, a listener of sound mind might reasonably be expected to act on your words in a violent manner.

Not any more. In the past year, the police have investigated more than 300 cases caused by someone taking offense online. In a tiny handful of instances, tweets sounded specific enough to constitute a threat — though the people posting them turned out to be harmless inadequates. In most cases, though, it was the insult that was deemed criminal. One man was jailed for tweeting vile comments about a recently murdered teacher, another for posting that all UK troops “should die and go to hell” when six soldiers were killed in Afghanistan.

These cases were unusual in that they led to convictions; most come to nothing. But that’s not the point. The effect of launching a police investigation, even if nothing follows, is to chill the atmosphere. I have had constituents taken to court for distributing Bible verses deemed offensive to gay people, for saying rude things about Muslims and — in one case on the Isle of Wight — for playing “Kung Fu Fighting” on the piano in the presence of a Chinese couple.