The prime minister, Boris Johnson, has been admitted to hospital for tests with persistent Covid-19 symptoms 10 days after being diagnosed with the illness.
Downing Street said the decision, which came at the end of a weekend in which health secretary Matt Hancock hinted at tougher measures to curb the spread of coronavirus, was a "precautionary" measure taken on the advice of Johnson’s doctor.
Johnson had been due to emerge from seven days' self-isolation on Friday, but remained behind closed doors because he continued to have a high temperature.
He has looked progressively worse during a series of video messages posted on Twitter since his diagnosis, but has continued to chair daily meetings and cabinet meetings on the pandemic via videolink.
A Downing Street spokesperson said: "This is a precautionary step, as the prime minister continues to have persistent symptoms of coronavirus 10 days after testing positive for the virus.
"The prime minister thanks NHS staff for all of their incredible hard work and urges the public to continue to follow the government’s advice to stay at home, protect the NHS and save lives."
Health secretary Matt Hancock was diagnosed with Covid-19 shortly before Mr Johnson, but managed to shake off the potentially-deadly bug and came out of isolation on Thursday.
Hancock warned yesterday that the government could introduce stricter lockdown measures if people do not comply with existing controls.
Speaking to Sky’s Sophy Ridge, he said sunbathing was against the rules and accused those out enjoying the weekend sunshine of “putting lives at risk”. He reiterated government guidance that people can only go outside for one period of exercise a day.
“It's quite unbelievable, frankly, to see that there are some people who are not following the advice, but the vast and overwhelming majority of people are,” he said.
And Hancock later told the BBC’s Andrew Marr that the government “might have to take further action” if people do not comply with the rules.
“I understand how difficult these measures are, of course I do. But the truth is the more people go out from home, the more the virus spreads,” he said.
“We’ve said because of the positive benefits to your physical and your mental health that it’s ok to exercise on your own or with members of your own household.
“But if the result of that is that too many people go out and flout the other rules because they say ‘well if I can exercise, then it’s fine for me to do other things’, then I’m afraid we will have to take action.”
But Hancock later rowed back from the comments, saying at the afternoon Downing Street conference that the government was “not planning any changes imminently”.