If Brexit has shown us anything, it is that the fabled unwritten British constitution — the subject of so much Bagehotian drivel — is a dead letter. Queen Elizabeth is head of state in name only, a kind of bejeweled notary public, and the prime minister, Boris Johnson, is merely the head of her government. His recent prorogation of Parliament in the hope of forcing a no-deal Brexit was declared null on Tuesday by the recently created Supreme Court of the United Kingdom, led by "Red" Brenda Hale, Baroness Hale of Richmond, with whom the British people are being told the buck ultimately stops.

This is lawless. Never in the history of the British Isles has the judiciary exercised any power over such decisions. The font of law is the monarch, who has given her assent to the prorogation upon the advice of her ministers. The Supreme Court's ruling is nonsensical on its face because it assumes a jurisdiction that it does not possess. The unwillingness of Britain's quasi-official establishment to assent to the will of her people on the European question has made them a nation of constitutional engineers. A reactionary like Johnson will not be able to match their ingenuity. His only hope is to look to the past rather than to the kritarchy envisioned by the BBC and the Guardian and the City.

As it happens, hidden away in the junk shops of British legal history there is a machine ably suited to the work that Johnson has undertaken: the office of Lord Protectorate, as exercised by Oliver Cromwell. Old Ironsides faced a somewhat similar predicament during the so-called Rump Parliament of 1651-1653, which refused to pass legislation necessitated by the disestablishment of the monarchy but would not dissolve or agree upon the date for a new election. Faced with constitutional paralysis that would have destroyed the country, Cromwell acted unilaterally, dissolving Parliament by force.

I am not necessarily suggesting that when John Bercow and Jeremy Corbyn and the other MPs report to the Commons on Wednesday they should be met by Johnson with 40 musketeers, or that Lady Hale should hide herself in an oak tree. But it does seem to me very seriously the case that unless the queen is willing to do something besides pet her dogs, the entire British constitutional order will collapse. If Johnson wins another general election, he must pass legislation that invests him with powers sufficient to direct the affairs of the nation by his own authority rather than that of the crown, which has all but abdicated. He must be able not only to complete Britain's withdrawal from the European Union but to undertake what Cromwell called the "healing and settling" of the nation following the anarchy of the last several governments — the making of generous new provision to British social services, the negotiation of trade deals with the United States and other allies, the creation of a new immigration policy, the reversal of the pub smoking ban, and so on, casting the kingdom old into another mould. If Johnson cannot or will not rule unilaterally, the unelected Supreme Court will do so instead. There is no middle option.

Did it have to be this way, I wonder? In many ways the distinction between the head of state, from whom all legal authority flows, and the head of government, who merely sits at the head of the monarch's advisers, seems to me an admirable one. It would certainly provide a solution to the numerous dilemmas faced by American opposition parties, who are periodically reminded of the fact that they cannot bring federal legal proceedings against the man who directs all federal law enforcement activity. The present weakness, though fatal, seems to me to have been unguessed. It was not the fault of the queen per se but of one of her previous advisers, David Cameron, the Conservative prime minister who cynically decided to put Brexit to a vote in the hope of making the issue disappear forever. The referendum itself was extra-legal, an innovation that should never have been attempted. Those who wished to see Britain withdraw from the European Union ought to have elected a parliamentary majority in support of such action.

This did not happen. But there is no retreating from the issue now. No government that attempts to ignore or to reverse the results of the 2016 vote will be regarded as legitimate; no government that attempts its implementation will be allowed to succeed because it lacks the authority to do so. The choice for Britain is between judicial supremacy and Roundhead Caesarism.

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