LONDON — Prime Minister Boris Johnson of Britain has always taken a seat-of-the-pants approach to governing. But his reversals this week on the two most pressing issues facing the country — the pandemic and Brexit — have been breathtaking, even by Mr. Johnson’s brashly improvisational standards.
On Wednesday, alarmed by a resurgence of the coronavirus, Mr. Johnson announced that the British government would ban gatherings of more than six people, after weeks of encouraging people to go back to work, eat out at restaurants, patronize pubs and send their children back to school.
Hours earlier, the government introduced legislation on Northern Ireland that would override a landmark Brexit agreement that Mr. Johnson himself struck with the European Union, shepherded through Parliament and championed during last year’s election on his way to a landslide victory.
The government admitted that this unexpected move breaks international law, which critics say raises a sticky question: Why should people obey Mr. Johnson’s new rules on social distancing when he brazenly flouts a legal treaty?
“It’s a madman, no-holds-barred style of governing,” said Mujtaba Rahman, an expert on Brexit at the political risk consultancy, Eurasia Group. “You put your foot on the accelerator as hard as you can and hurtle yourself towards the cliff.”
Whether Mr. Johnson’s brinkmanship with the European Union will crash the current trade negotiations or enable him to strike a better deal was not yet clear. European officials demanded urgent talks with Britain about its threat to rewrite the parts of the Withdrawal Agreement that deal with Northern Ireland. But they did not break off another set of talks in London for a trade deal.
Either way, Mr. Johnson’s moves showed a readiness — one that dates back to his days as the mayor of London — to shift course suddenly, contradict himself and thumb his nose at traditional norms in pursuit of his goals. And, as so often in the past, his methods drive many in Britain’s establishment to distraction.
One of his Conservative predecessors, John Major, said of the Brexit reversal, “If we lose our reputation for honoring the promises we make, we will have lost something beyond price that will never be regained.”
Mr. Johnson’s about-face on lockdown rules was a clearer case of bowing to evidence that the virus is spreading. After a tranquil stretch in June and July, new cases began to creep up in August. By last Sunday, they had spiked to nearly 3,000, the highest daily number since May 23.
Health officials said they worried that many of the cases were in young people, raising the danger that Britain is on the same path as France and Spain, where a jump in cases prompted Britain to impose a travel quarantine on both countries.
The country’s infection rate has risen from 12.5 per 100,000 people last week to 19.7 per 100,000, indicating that the “R number” — a measurement that shows how many people are being infected on average by each person with the virus — has risen above one, a critical threshold.
“It’s a stitch in time to save nine,” Mr. Johnson said at a news conference, flanked by his chief medical and scientific advisers. “These measures are not another national lockdown. The whole point of them is to avoid a new national lockdown.”
Health experts praised Mr. Johnson for imposing modest restrictions now, rather than risking a larger spike, which would necessitate more draconian measures. But they said Britain’s policies continued to be inconsistent. Authorities allowed a crowd to gather for the opening day of horse races on Wednesday in Doncaster, in northern England, before abruptly closing the rest of the races to spectators.
“The U.K. government is muddled and needs to decide on a clear strategy because in the current approach, both the health and the economy will suffer, and compliance by the public will continue to fall,” said Devi Sridhar, professor and chairwoman of global public health at the University of Edinburgh.
The mixed messages reflect a lingering tension within Mr. Johnson’s cabinet and party between those who worry about a deadly second wave of infections this fall and winter and those who argue that more lockdowns will throttle the economy. Even now, Mr. Johnson insisted that schools would stay open and that people should still consider returning to work, as long as it was safe.
Critics also fault the government for failing after months to organize an efficient national test-and-trace program. The Labour Party leader, Keir Starmer, confronted Mr. Johnson in Parliament on Wednesday with stories of people who were told they would have to travel hundreds of miles to get a test.
The government said the police would levy fines of 100 pounds, about $130, on people who violated the six-person limit. But Mr. Johnson deflected questions about whether he intended to “cancel Christmas,” a phrase that suggests the difficult decisions the government will face on the virus as the fall and winter set in.
For Mr. Johnson, analysts said, picking a fight with the European Union was a lot easier. Tim Bale, professor of politics at Queen Mary, University of London, said that in escalating the language on Brexit, Mr. Johnson had reverted to a tested strategy that played to the hard-core Brexit base in the Conservative Party.
While Mr. Johnson’s threat to renege on a treaty has outraged commentators and establishment figures like Mr. Major and former Prime Minister Theresa May, the government seems to have calculated it will cause little blowback beyond political circles in Westminster.
“They seem to regard breaking international law as a Beltway issue rather than something that will bother most people — and in that, they are almost certainly right,” Professor Bale said, referring to the parochial politics of Washington.
Still, antagonizing the European Union four months before the deadline for a trade agreement is not without risks. Mr. Rahman said he now believes there is a greater than even chance that Mr. Johnson will fail to strike a deal with Brussels, ushering in a period of disruption on top of the pandemic.
Having promised in the election to “get Brexit done,” analysts said, Mr. Johnson is also taking a risk in prolonging the wrangling, as many Britons are simply sick of hearing about it. In January, if the fears of scientists are true, he could find himself dealing with a far more serious health crisis.
“Covid is a much bigger challenge and the political risks of being seen as incompetent are much greater,” Professor Bale said. “Most voters are far more worried about Covid, which impacts on them directly, than the technicalities of legal interpretations.”