Prime Minister Boris Johnson has been moved to intensive care after his coronavirus symptoms worsened.
Mr Johnson, 55, was admitted to St Thomas’ hospital in central London on Sunday after his coronavirus symptoms persisted for 10 days.
Having been in hospital for tests and observation, his doctors advised that he be admitted to intensive care on Monday evening.
Mr Johnson is understood to be conscious and was moved to intensive care at about 7pm as a precaution should he require ventilation to aid his recovery.
Foreign Secretary Dominic Raab will “deputise where necessary”, a Number 10 spokesman said.
A Number 10 spokesman said: “Over the course of this afternoon, the condition of the Prime Minister has worsened and, on the advice of his medical team, he has been moved to the intensive Care Unit at the hospital.
“The PM has asked Foreign Secretary Dominic Raab, who is the First Secretary of State, to deputise for him where necessary.
“The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication.”
The Prime Minister’s official spokesman said on Monday morning that Mr Johnson had been taken to hospital on the advice of his doctor and as a “precaution”, and that it was not an emergency admission.
It came just a few hours after Mr Raab told a press briefing that the PM remained in charge of the Government despite remaining under observation.
At a press conference less than two hours before the decision was made, Mr Raab told a press briefing that the PM remained in charge of the Government despite remaining under observation.
Earlier in the afternoon, Mr Johnson tweeted: “Last night, on the advice of my doctor, I went into hospital for some routine tests as I’m still experiencing coronavirus symptoms. I’m in good spirits and keeping in touch with my team, as we work together to fight this virus and keep everyone safe.
“I’d like to say thank you to all the brilliant NHS staff taking care of me and others in this difficult time. You are the best of Britain.”
At the daily Number 10 news conference on Monday Mr Raab faced repeated questions as to how Mr Johnson could cope with demands of the premiership if he was sick enough to require hospital treatment.
Downing Street, which had previously described his symptoms as “mild”, switched to describing them as “persistent”.
They included a cough as well as a continuing high temperature, 10 days after he first tested positive for the coronavirus.
Mr Raab said he had last spoken to the PM on Saturday – almost 48 hours before being sent to brief the nation his well-being and efforts to tackle Covid-19.
Mr Johnson’s fiancee Carrie Symonds previously said she had been suffering Covid-19 symptoms, but is “on the mend”.
Ms Symonds, 32, who is expecting the couple’s first baby in early summer, said she was not tested for the virus.
Health Secretary Matt Hancock is already back at work after having tested positive for Coronavirus.
And Chief Medical Officer Professor Chris Whitty returned to work on Monday after developing symptoms and the Prime Minister’s chief adviser, Dominic Cummings, has also self isolated.
Responding to the news, Labour leader Sir Keir Starmer tweeted: “Terribly sad news. All the country’s thoughts are with the Prime Minister and his family during this incredibly difficult time.”
And Chancellor Rishi Sunak tweeted: “My thoughts tonight are with @BorisJohnson and @carriesymonds. I know he’ll be getting the best care possible and will come out of this even stronger.”
Sir Lindsay Hoyle, Speaker of the House of Commons, said: “This is terrible news. I know the thoughts and prayers of everyone across the House are with the Prime Minister and his family right now.
“We all wish him a speedy recovery.”
Meanwhile, the latest official figures showed 5,373 patients have died in hospital after testing positive for coronavirus in the UK as of 5pm on Sunday – an increase of 439 on the previous day.