Boris Johnson has been moved to intensive care after his coronavirus symptoms worsened.
What does this mean and will he continue to lead the country's response to the pandemic?
– Why has Mr Johnson been moved to the intensive care ward?
A Downing Street spokesman said the Prime Minister's condition had "worsened" on Monday afternoon.
On the advice of his medical team, the 55-year-old has been moved into the intensive care unit at St Thomas' Hospital in London, where he was admitted on Sunday evening.
Elections Henley Boris JohnsonJournalist Boris Johnson speaks at the count in Watlington, Oxfordshire, after winning the Henley seat for the Conservatives in the 2001 General Election. The seat was Michael Heseltine's, who has stepped down at this election.
He is understood to be conscious and was moved as a precaution should he require ventilation to aid his recovery.
– What treatment do coronavirus patients receive in intensive care?
Professor Derek Hill, Professor of Medical Imaging at University College London (UCL), said that many patients suffering from Covid-19 need help breathing.
Ventilators can be invasive, which involves a tube being put down the patient's throat, or non-invasive – such as breathing through a specialised mask.
Mechanical ventilation tends to be recommended for coronavirus patients, Prof Hill said.
– Who will lead the Government?
The Prime Minister's official spokesman said that Foreign Secretary Dominic Raab would take over if Mr Johnson was unable to work due to illness.
On Monday evening, after the Prime Minister was admitted to intensive care, Downing Street said that Mr Johnson had asked Mr Raab to "deputise where necessary".
Prior to his admission to intensive care, Mr Johnson had remained in charge of the Government, but Mr Raab chaired the daily Covid-19 meeting for ministers and officials on Monday morning.
– What would happen if Mr Raab also became ill?
The Prime Minister's official spokesman has previously confirmed that should Mr Raab also fall ill, Mr Johnson has the power to delegate responsibility to any of his ministers.
– When was Mr Johnson first admitted to hospital?
The Prime Minister was transferred to hospital as a "precautionary measure" on the advice of his doctor on Sunday evening.
Number 10 said that, 10 days after his positive test for Covid-19, Mr Johnson was still suffering a high temperature.
On Monday afternoon, before being transferred to intensive care, Mr Johnson said on Twitter he had gone into hospital for "some routine tests" but added he was in good spirits.
– Has Mr Johnson been working since his diagnosis?
Mr Johnson has led several meetings via video conferencing since his diagnosis including the Cabinet.
He has shared several video updates from his Number 11 flat and stepped outside to join the nationwide clap for NHS staff on Thursday evening.
– Has his pregnant fiancee been ill?
Carrie Symonds, who is expecting the couple's first baby in early summer, said she had been suffering Covid-19 symptoms but is "on the mend".
The 32-year-old tweeted on Saturday: "I've spent the past week in bed with the main symptoms of Coronavirus. I haven't needed to be tested and, after seven days of rest, I feel stronger and I'm on the mend.
"Being pregnant with Covid-19 is obviously worrying. To other pregnant women, please do read and follow the most up to date guidance which I found to be v reassuring."
She had previously shared a picture of her self-isolating in south London – away from Downing Street – with the couple's dog Dilyn.
– Has anybody else in Government been ill?
Health Secretary Matt Hancock, leading the country's response to the outbreak alongside the Prime Minister, returned to work last week having tested positive for Covid-19.
He said he had experienced mild symptoms and had worked from home while self-isolating.
England's chief medical officer Professor Chris Whitty made his first public appearance at Monday's press briefing after suffering from symptoms of the virus.
Scotland Secretary Alister Jack also developed telltale signs of the illness, while the Prime Minister's chief adviser Dominic Cummings has also been in self-quarantine after developing symptoms.