LONDON — When Boris Johnson was campaigning for Britain to leave the European Union in 2016 — a path that many experts warned would end in disaster for the country — one of his close allies, Michael Gove, famously declared that “people in this country have had enough of experts.”

Now, Mr. Gove and Mr. Johnson are leading the British government as it confronts the calamity of the coronavirus, and Mr. Johnson, now the prime minister, insists the process is being guided by experts. The trouble is, those experts can often disagree with each other or change their minds about the right course of action.

That messy back-and-forth has been on vivid display this week with the publication of a startling new report on the virus from a team at Imperial College in London. The report, which warned that an uncontrolled spread of the disease could cause as many as 510,000 deaths in Britain, triggered a sudden shift in the government’s comparatively relaxed response to the virus.

American officials said the report, which projected up to 2.2 million deaths in the United States from such a spread, also influenced the White House to strengthen its measures to isolate members of the public.