Boris Johnson was admitted to hospital on Sunday for precautionary tests as Downing Street said the prime minister was still suffering from persistent symptoms of coronavirus.
Mr Johnson, who first developed signs of the virus 10 days ago, has continued to run the government despite appearing to be unwell in some of his video messages.
On Friday he said in a video that he was “feeling better” despite not having fully recovered.
“On the advice of his doctor, the prime minister has tonight been admitted to hospital for tests,” said a Downing Street spokesperson on Sunday. “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 spokesperson said Mr Johnson thanked National Health Service staff for their “incredible hard work” and urged the public to keep following the government’s advice to stay at home to minimise the spread of Covid-19.
Aides added it was not an emergency admission, saying Mr Johnson remained in charge of the government and was in contact with ministers and officials.
Ministers said they were glad that the 55-year-old prime minister had admitted he needed more medical help.
“This may be the jolt, the wake-up call that he realises he has to rest to recover,” said one cabinet minister. “He will have been very reluctant to go to hospital.”
Conservative MPs expressed concern that Mr Johnson was more ill than Downing Street had suggested.
One senior MP said: “It’s absolutely against Boris’ character to admit himself to hospital . . . The WhatsApp groups [of Tory MPs] are full of people concerned about his health and who is going to fill the gap while he recovers.”
If he becomes too ill to work, Dominic Raab, foreign secretary and first minister of state, is expected to fill in for Mr Johnson.
With Mr Johnson due to stay in hospital overnight, Mr Raab will chair the daily meeting on Monday of ministers and officials who oversee the government’s response to the pandemic.
Should Mr Johnson remain in hospital for further days, Mr Raab would probably oversee more of his duties.
But Whitehall officials stressed there is no official pecking order of ministers to determine who will stand in for Mr Johnson.
In the daily Downing Street press conferences on coronavirus, Number 10 has put forward health secretary Matt Hancock and Cabinet Office minister Michael Gove as stand-ins for the prime minister while he has been in self-isolation.
These ministers, along with Mr Raab, are likely to lead the media briefings while Mr Johnson recovers.
Mr Johnson has sought to present a cheery front throughout his illness, telling the public that he would use the “wizardry of modern technology” to keep in close touch with colleagues and thereby continue to lead efforts to deal with the virus.
He first developed mild symptoms of coronavirus on March 26, and by the following day he was confirmed as the first G7 leader to be infected with Covid-19.
Subsequently, Mr Hancock also tested positive for the virus although he is now fully recovered and back at work.
Chris Whitty, the chief medical officer for England, went into self-isolation after displaying symptoms of Covid-19.
The prime minister’s partner Carrie Symonds, who is at least six months pregnant, has also had symptoms of the virus.
“I’ve spent the past week in bed with the main symptoms of coronavirus,” she said on Twitter. “I haven’t needed to be tested and, after seven days of rest, I feel stronger and I’m on the mend.”
On Sunday evening, there were expressions of goodwill from across the political spectrum for Mr Johnson.
Shadow health secretary Jonathan Ashworth said he looked forward to seeing the prime minister healthy and well again. “I send my very best wishes to Boris Johnson and his family tonight for a swift recovery,” he added.
Mr Hancock confirmed earlier on Sunday that a further 621 people had died from coronavirus in the UK, taking the total number of victims to 4,934.