Slightly as I expected, in asking where the Met’s Defence Council authorisation to carry pepper spray or CS was, I was missing something. I assumed it would be an obscure Amendment Act or similar, but it turned out to be a giant elephant in the room.

The reason why police are exempt, pointed out by an anonymous commenter, is that unless specifically stated, Acts of Parliament do not apply to the Crown.

This astonishing principle of British jurisprudence derives from the constitutional formality that laws are made in the name of the monarch, and indeed enacted only by her permission, a stage of the legislative process called Royal Assent. As one writer puts it, “since laws are made by rulers for subjects, a general description of those bound by a statute does not include the Crown.” Laws are for peasants.

This staggeringly feudal attitude would be bad enough if it just meant Her Maj not paying her TV Licence. But the modern interpretation of “the Crown” extends much further.

The Firearms Act itself identifies police officers, their staff, and military servicepeople as “servants of the Crown.” That police, placed in a position of authority over us, are not subject to the same laws as the rest of us should be intolerable.

Not only does this relic mean a double standard between us and those that police us, it extends a double standard throughout society. The modern Crown institution isn’t a handful of people gathered round a throne – it is a state, and that brings the Crown into every area of the national life.

For example, in Lord Advocate vs Dumbarton District Council we learn that private contractors working for the Ministry of Defence were entitled to obstruct the road without permission because the Crown is not bound by the Roads (Scotland) Act 1984 or the Town and Country Planning (Scotland) Act 1972.

The modern Crown can be interpreted to include a huge panoply of state agencies, state enterprises such as the BBC or the Post Office, and, increasingly, private adjuncts to the state such as the Dumbarton contractors or the owners of a PFI NHS hospital.

What appears an obscure and ceremonial constitutional nuance thus becomes an ubiquitous source of two-track law. Rules for the ruled but not for the rulers.

It is an alien concept in any modern constitution – when Richard Nixon said “when the President does it, that means it’s not illegal,” he was wrong. In our backward system he’d have been right.

What began for me as a question about a missing of piece of paperwork from the MoD has brought me face-to-face with a fundamental flaw in our constitution. It’s comforting to believe that our monarchy is purely ceremonial and that we live in a modern democracy. But in an ever-growing list of ways I’m learning that that is very far from the truth.