LONDON — What if Britain’s Parliament voted to remove Prime Minister Boris Johnson from office and he refused to leave, igniting a constitutional crisis?
This is not some far-fetched theory. The possibility of Mr. Johnson refusing to step down was reported to have been raised recently by his top deputy and strategist, Dominic Cummings.
As the country girds for Parliament’s return in September, only one thing seems certain: The confused and chaotic Brexit process promises to plunge Britain into new unknowns as an Oct. 31 deadline for leaving the European Union bears down.
The British political system may yet withstand the tumult. But scholars say it has been more than a century since the country’s constitution — a medley of laws and customs, many but not all of them written — has come under such strain.
The British news media is filled daily with speculations about once unthinkable political ploys, reminiscent to some analysts of President Trump’s norm-shattering machinations in Washington. They center on whether Mr. Johnson will run roughshod over the conventions and traditions embedded in the constitution in his single-minded pursuit of Brexit, “come what may.”
“I think this is an entirely new constitutional situation,” said Robert Saunders, a historian at Queen Mary University of London. “The British haven’t thought it necessary to think seriously about the constitution for quite a long time.”
Suddenly, armchair constitutional theorizing is in vogue. Fantasies about Queen Elizabeth II stepping in are occupying serious space even on The Times of London’s letters page, where last week Malcolm Rifkind, a former foreign secretary, suggested that the sovereign consider firing Mr. Johnson to stop “the gravest constitutional crisis” since King Charles I tangled with Parliament in the 1600s.
“King Charles lost his head by flouting the constitution,” Mr. Rifkind wrote. “Mr. Johnson will wish to keep his, while some around him are, clearly, losing theirs.”
It all begins with signals from some lawmakers that when Parliament reconvenes in September, it will pass a vote of no confidence in Mr. Johnson’s government, based on his intention to pull Britain out of the European Union by Oct. 31, “do or die,” deal or no deal.
Traditionally, that would stop a government in its tracks. These days, lawmakers have 14 days after such a vote to try to put together a new government. If they cannot, the prime minister is then supposed to call a general election.
But as Mr. Cummings has let it be known, even if a rival were to attract enough support to form a government, the prime minister could legally call for a general election and refuse to vacate Downing Street. The Fixed-Term Parliaments Act of 2011, which guides the procedures for a no-confidence vote, does not specifically require prime ministers to step aside at that point, even if custom and respect for democratic norms would seem to dictate that they should.
At this point, constitutional experts say, the queen could conceivably step in and dismiss Mr. Johnson, using her “reserve prerogative power.”
Given the queen’s lifetime of studied neutrality, that is considered unlikely, though not impossible — the queen’s aides have already been talking with Mr. Johnson’s about how to navigate the clamor for her to step in.
Under Mr. Cummings’ scenario, Mr. Johnson could sit tight and schedule an election for after Brexit, sending the country crashing out of the European Union on Oct. 31 and in the middle of a campaign.
If that were to happen, it would run afoul of the civil-service code, which forbids any major policy changes during an election campaign, on the assumption that an incoming government would want to have its say on the matter.
There is considerable debate about whether Mr. Johnson is really planning to hop the constitutional guardrails or is simply threatening to do so for the sake of political leverage.
He may be trying to persuade European leaders to offer friendlier terms on a new Brexit deal by showing that he is serious about leaving without one, analysts say. And he may be trying to show British lawmakers the folly of trying to boot him from office, given the threats that he would ignore them anyway.
Others have said that if Mr. Johnson is sincere in his threats to call a general election and crash out of the European Union on Oct. 31, that could mean conducting a campaign in the midst of economic chaos, shortages of food and medicine, and secession threats in Scotland and Northern Ireland — not exactly the most attractive political terrain for the incumbent Conservatives.
Perhaps that is what Dominic Grieve, a Conservative lawmaker and former attorney general, had in mind when he called the idea of Mr. Johnson squatting in Downing Street “breathtaking, stupid, infantile, and it won’t work.”
However that comes out, the worry of some scholars is that Britain’s mishmash of laws and customs can no longer restrain lawmakers bent on engaging in constitutional chicanery.
The prime culprit in these scenarios is the Fixed-term Parliaments Act and its failure to specify the resignation of the prime minister after a no-confidence vote and the formation of a new government.
“This was a really significant constitutional change for which there was a quite powerful intellectual case, but it was rushed through with seemingly little thought about how it would work under particular circumstances,” Mr. Saunders said.
The public face of the new government’s brinkmanship, Mr. Cummings, served previously as a mastermind of the 2016 Brexit Leave campaign. With his disdain for politicians of all stripes, Mr. Cummings has emerged as a Rasputin-like character by Mr. Johnson’s side, leading his boss in taking a machete to the norms and conventions of British politics in their charge toward Brexit.
It is this camp’s scorn for constitutional safeguards, some scholars say, more than any underlying weakness in the system, that has put Britain on the edge of a crisis.
“All political systems ultimately rely on people being willing to play by the rules,” said Robert Hazell, a professor of government and the constitution at University College London. Professor Hazell said that held true for Britain’s partly written constitution, just as it did for more heavily codified systems like that of the United States.
As in the United States, Britain is coming to realize that many of its democratic norms and practices depend upon the good will of those in power.
“There are many similarities between Johnson and Donald Trump, not least their willingness to bend the rules or, in many cases, what have been regarded as the rules but are in fact longstanding conventions,” Professor Hazell said.
In some ways, the British system has become more like the American one — and more susceptible to the same workarounds — as lawmakers have codified more of it, Mr. Saunders, the historian, said.
Now that some laws, like the Fixed-term Parliaments Act, are written down, they are treated as having extra authority, inviting attempts to scrutinize their language and wring whatever meaning out of them suits a certain side.
As for the conventions that remain unwritten, some have started claiming that they no longer apply. It has long been assumed, for example, that the queen does not veto legislation. But some right-wing commentators have suggested that Mr. Johnson should tell her to refuse to sign any laws blocking a no-deal Brexit, on the grounds that the 2016 referendum on European Union membership holds more democratic weight than any laws passed by Parliament.
That exposes what many scholars see as the fundamental constitutional pickle facing Britain.
The 2016 referendum, they say, created rival mandates: one stemming from the public vote for Brexit, the other from the lawmakers Britons elected to carry out that decision. Parliament created more confusion by deciding soon after the referendum to set the clock ticking on Britain’s departure, without considering what it would look like.
“Parliament has ruled the end, but not the means,” said Vernon Bogdanor, a professor at King’s College London.
It is that political vacuum that has spawned fantasies of the queen stepping in to rescue one side or another from the grips of a constitutional crisis.
“It’s uncharted waters,” Mr. Saunders said. “It’s always been assumed the government wouldn’t put her in a position to make a politically contentious decision. But that looks like it may change.”