As recently as Friday, the UK prime minister said he was “feeling better”, but that he would remain in self-isolation until his temperature dropped.
However, on Sunday evening Downing Street revealed he had been taken to hospital for precautionary tests.
It is not believed to be an emergency admission though the PM is expected to stay in overnight, having thought to have been admitted in the early evening.
“On the advice of his doctor, the prime minister has tonight been admitted to hospital for tests,” a spokeswoman 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.”
Johnson has been continuing to the lead the Government’s response to the COVID-19 crisis from inside Downing Street, chairing Cabinet meetings via video link.
He is understood to be in an NHS hospital in London, where he will stay for “as long as needed”.
A Number 10 spokesman insisted on Sunday he remained “in charge of the Government” and has not handed responsibilities to his de facto deputy Dominic Raab.
However, Mr Raab is likely to chair the daily COVID-19 meeting on Monday morning for ministers and officials instead of the PM.
Latest coronavirus news, updates and advice
Johnson has shared several video updates from his Number 11 flat since his diagnosis, and joined the nationwide clap for NHS staff on Thursday evening.
He has not been seen publicly since, although he spoke to new Labour leader Sir Keir Starmer on Saturday afternoon.
In his social media post on Friday, Johnson looked and sounded tired as he said: “Although I’m feeling better and I’ve done my seven days of isolation, alas I still have one of the symptoms, a minor symptom, I still have a temperature.
“So, in accordance with government advice I must continue my self-isolation until that symptom itself goes.”
Johnson has repeatedly urged people not to break social distancing rules as the weather warms up, even if they were going “a bit stir crazy”.
His pregnant fiancee, Carrie Symonds, has also been suffering from coronavirus symptoms. On Saturday, she said she was “on the mend” after spending all week in bed.
‘Thoughts with the PM’
Johnson received messages of support from across the political spectrum.
The Labour leader Sir Keir Starmer wished the PM a “speedy recovery” after the announcement.
Jeremy Hunt, the former Health Secretary who has been critical of the government response, said: “Thoughts with Boris Johnson this evening.
“Whatever political persuasion the whole country is united in wanting our PM to get fit and well as soon as possible #BackBoris.”
Labour MP Jess Phillips tweeted: “Sending regards to the Prime Minister and his family and friends especially to Carrie, it must be such a worry.”
Johnny Mercer, the Conservative MP for Plymouth, Moor View, tweeted a picture of himself with the Prime Minister with the message “Get well soon mate” followed by a red heart.
Queen’s message of hope
The news emerged shortly after the Queen gave a rare address to the nation on Sunday night, in which she said if we “remain united and resolute” in the face of the coronavirus outbreak “we will overcome it”.
The head of state warned the country, in lockdown for almost two weeks and with thousands dead after contracting Covid-19, “may have more still to endure”.
Read more: Queen’s message of hope to the UK
In a rare televised address to the country and Commonwealth, the Queen sounded a positive note after what has been an unsettling period, saying: “We will succeed – and that success will belong to every one of us.”
On Sunday, the Government revealed the coronavirus death toll had risen by 621, a slight fall on yesterday when 708 people were confirmed to have died from COVID-19 over the last 24 hours.
It means a total of 4,934 patients have died in hospital having contracted COVID-19 as at Saturday 5pm.