London — Britain's Department of Health and Social Care declared the coronavirus outbreak a "serious and imminent threat" to public health on Monday, increasing its powers to keep people quarantined but stressing that the overall risk level to the British public remained "moderate."

"The risk to the public has not changed," the department announced on Twitter. "This is a legal term which we announced this morning as part of changes to make it easier for health professionals to do their job."

The risk to the public has not changed. This is a legal term which we announced this morning as part of changes to make it easier for health professionals to do their job. The NHS is well prepared to deal with #coronavirus. More info 🔽 https://t.co/PozW8fZn61 pic.twitter.com/QOw1bNcYrO — Department of Health and Social Care (@DHSCgovuk) February 10, 2020

According to the BBC, a British citizen who was on the first evacuation flight back to the U.K. from Wuhan, China — the center of the current outbreak — threatened to leave quarantine, and health care providers wanted to be able to prevent him from doing so.

Get Breaking News Delivered to Your Inbox

"One of the people who was on a flight back from Wuhan and is currently being held in isolation on Merseyside (near Liverpool) is threatening to abscond," BBC political correspondent Iain Watson said, adding: "They brought in these new regulations to try and compel him to stay put."

Britain's Foreign Office organized two flights to evacuate its citizens from Wuhan, and the evacuees are currently quarantined at two locations in the U.K.

Those on the first flight reportedly signed contracts that committed them to spending 14 days in isolation upon their return, according to the BBC, but those contracts do not give authorities the power to prevent them from leaving early, as the one man is reportedly threatening to do. The new powers allow authorities to compel people to remain in isolation or forcibly put people in isolation if they are deemed a threat.

Four more cases of the new coronavirus were confirmed in the U.K. on Monday, bringing the total up to eight.

Between 1% and 5% of those infected with the virus outside of China may die from it, according to research released Monday by infectious disease specialists at Imperial College, London, who are working with the World Health Organization.

"Our estimates — while subject to much uncertainty due to the limited data currently available — suggest that the impact of the unfolding epidemic may be comparable to the major influenza pandemics of the 20th century," said Profession Neil Ferguson, one of the authors of the report.

"It is therefore vital that countries across the world continue to work together to accelerate the development and testing of effective treatments and vaccines, on the fastest possible timescale."