If you really wanted to, you could write down all of them, and this document would be Britain’s constitution—on that day. But with the government and opposition using every lever at their disposal, it might be out of date by the time it came off the press.

Of course, the U.K. does have foundational documents that stand the test of time. The 1689 Bill of Rights established the supremacy of Parliament over the Crown after the Glorious Revolution overthrew King James II. (For this and many other reasons, talk of Britain—or, more accurately, England—being somehow more coolheaded, more conservative, than other countries is absurdly ahistoric: England executed its monarch, King Charles I, more than 100 years before the French.)

The fundamental tenet of the British constitution, then, is that Parliament is sovereign—and therefore no Parliament can bind the next. What one Parliament does, another can undo. Parliament, elected by the people, can change its mind, reverse course—or double down. It can kill the King if it wants. True, the current Queen might have recourse to the law if Parliament tried to pull an Oliver Cromwell today. But essentially, this constitutional settlement has not changed: Parliament’s sovereign power remains the core principle governing Britain.

Let’s take one piece of legislation that, on the face of it, appears to change the nature of this constitutional settlement: the 1972 European Communities Act. This made Britain part of the EU, making European law, made in Brussels, supreme over British law, made in Parliament. Yet even this, as we are seeing today, can be repealed. Parliament remains sovereign.

There are other complicating factors: the Human Rights Act, the Good Friday Agreement, and devolution. Britain is also, theoretically, bound by international law, though Parliament could always legislate to become a European North Korea if it wished. It is sovereign.

Much of the rest of the British constitution is legislation, case law, and convention. This means the U.K. has been, traditionally at least, supremely flexible in how it governs itself. In World War II, for instance, both main parties agreed to delay a general election until after the cessation of hostilities. This meant that even though the convention was to hold elections every five years, there was no election for 10 years, from 1935 to 1945. In that time, the premiership changed hands twice: from Stanley Baldwin to Neville Chamberlain in 1937, and from Chamberlain to Winston Churchill in 1940. This was all entirely constitutional.

Ultimately, the core convention is that whoever controls Parliament holds power. This takes us back to Brexit. The problem is, since 2016, no one has really controlled Parliament. In a fractious, historic debate yesterday—largely centered on this very question—the former Conservative Attorney General Dominic Grieve, who has since been kicked out of the party for voting against the government, set out the nub of the issue. “Our constitution is adaptable,” he told MPs. “And I’m afraid it is having to adapt to the reality that our government does not have a majority and has not had one for some time.”