As a law professor, I can see Boris Johnson hasn't committed a crime – he's done something far worse than that

The Supreme Court has crushed Boris Johnson's assault on the constitution. The only thing for him to do is resign

Three years ago, Boris Johnson argued Britain should vote Leave, taking back control and “freeing” the UK from the European Court of Justice to make the British Supreme Court its top judicial body. Today, that same Supreme Court has given Johnson the most devastating verdict issued in a generation, and it’s left his premiership in tatters.

Johnson's government prorogued parliament for five weeks. They argued that the extended suspension was simply needed to put together a new legislative agenda for a Queen's Speech next month, and that this was a political decision beyond review of the courts, meaning that any such intervention would be an act of judicial interference.

In its landmark decision, the Supreme Court has found the government wrong on all points. Its damning, unanimous verdict is that "it is impossible for us to conclude on the evidence … that there was any reason – let alone a good reason – to advise Her Majesty to prorogue parliament for five weeks". Lady Hale, president of the Supreme Court, declared that Johnson's actions were "unlawful, void and of no effect".

The legal implications are clear: when Black Rod came to the House of Commons to suspend it, the order was a mere "blank piece of paper" as its words had no lawful effect. Parliament was not technically suspended, and should now be reconvened immediately in a manner to be determined by the speakers of each house.

The repercussions of this verdict are profound, and given the unanimous verdict, they will run deep. The prime minister has been declared to have made an unlawful request to the Queen to silence parliament in order to pursue a policy agenda that parliament was trying to block. This is not simply undemocratic in that it gags Britain’s elected representatives; it's also unconstitutional.

Amongst lawyers and legal commentators, it was widely expected the government would lose. The executive simply cannot avoid unwelcome scrutiny by parliament, to which it is accountable, by suspending it in order to get its way by other means. The UK may have an "unwritten" constitution insofar as its central rules and conventions are not set out in one document as they are in the US, but its rules and conventions are no less real and form the basis for the rule of law.

So what now? There is a clear convention to be followed by senior government officials when found to have breached the law: to resign immediately. Johnson may not have committed a criminal offence, but in committing an offence against our constitution and the rule of law, he has arguably done something even worse – not only damaging the office of the prime minister, but dragging the Queen into his Brexit mess.

Johnson's time is now up. He has made a serious error of legal judgement, and he must face the consequences. Clinging onto his office will not improve his position, whether in parliament or in trying to represent the country abroad as he tries to secure a new Brexit deal.

Whether one supports Leave or Remain is irrelevant; the rule of law was always going to prevail. In spite of the of the prime minister’s constitutional vandalism, it has done so triumphantly. Johnson must now pay the price and become the UK's shortest serving occupant of 10 Downing Street. And the sooner, the better.

Thom Brooks is Professor of Law and Government at Durham University.