On the Today programme this morning, the Metropolitan Police Commissioner, Sir Paul Stephenson, was defending the police handling of yesterday's student protests.
Asked about the idiotic attack by protesters on the car carrying the Prince of Wales and the Duchess of Cornwall, he praised the "restraint" of the firearms officers who were present.
The implication appeared to be that, but for this "restraint", the protesters would have been shot dead properly. The commissioner furthermore described the restraint of his officers generally, not by reference to the officers following training, policies and procedures, but in terms which meant he could commend the officers' moral qualities.
The impression one formed, listening to Stephenson, was that it is a matter of simple discretion for his officers not to be more heavy-handed, or even lethal, in dealing with protesters. Any lapse would be understandable, and merely a moral failing of the officer.
One test of a liberal society is the point at which killing protesters becomes acceptable, at least to those with the power to do the killing.
This morning it seemed clear that, unless the commissioner misspoke, or one simply misinterpreted him, that point is now at the discretion of any police officer with a gun.
David Allen Green is a lawyer and writer. He is legal correspondent of the New Statesman and was shortlisted for the blogging section of the Orwell Prize in 2010.