Boris Johnson will continue commanding the response to the coronavirus pandemic while isolating in Downing Street after testing positive for the disease.
Two of his key lieutenants will also remain in self-isolation on Saturday, after Health Secretary Matt Hancock also confirmed he has Covid-19 and Professor Chris Whitty exhibited symptoms.
The dramatic developments came as a total of 759 people died in UK hospitals after being diagnosed with the virus, while 14,543 tested positive and tens of thousands more are thought to be infected.
It is highly likely that Prof Whitty, who is England's chief medical officer, will be awaiting results of his own test for the virus, while other key figures will be wary of developing symptoms.
The PM, who was struck by a high temperature and persistent cough, will continue leading efforts to slow the virus's spread behind the closed doors of his flat above No 11.
The 55-year-old faced allegations of failing to follow his own guidance for not spreading the disease by practising social distancing.
Concerns are rife over who at the heart of Government could be stricken next, with Chancellor Rishi Sunak having been with the PM shortly before he tested positive.
Cabinet Secretary Sir Mark Sedwill was also with the PM, Mr Hancock and Prof Whitty at a Cabinet meeting on Tuesday.
Neither the Chancellor or Sir Mark had displayed symptoms on Friday night and therefore had not been tested and were not in isolation.
Both the PM and Mr Hancock were only showing "mild symptoms" of the disease but would have to spend seven days in isolation.
Mr Johnson noticed symptoms on Thursday afternoon before receiving the test results at midnight.
At the latest of the daily press conferences, Cabinet minister Michael Gove declined to be drawn on whether MPs had been too slow in practising social distancing.
He instead said the diagnosis of Mr Johnson and Mr Hancock showed the "virus does not discriminate", warning: "We are all at risk."
By Mr Gove's side, NHS England chief executive Sir Simon Stevens said testing would begin on NHS staff for coronavirus from next week, following widespread concern.
He also announced that he had given the go-ahead to two new temporary hospitals being built in Birmingham and Manchester to join the facility under development in London.