Boris Johnson and his key lieutenants in the battle against coronavirus were all fighting the illness as it struck at the heart of Government on Friday.
The Prime Minister and Matt Hancock, the Health Secretary, both tested positive for the virus, with Chris Whitty, the chief medical officer, in isolation with clear symptoms.
Rishi Sunak, the Chancellor, was working from home as a precaution after taking part in the Clap For Carers event with Mr Johnson in Downing Street on Thursday night.
Duncan Selbie, the head of Public Health England, also revealed that he was self-isolating after developing symptoms last weekend.
Mr Johnson – the first world leader to test positive for the virus – insisted he remained well enough to run the country via telephone and video link from Downing Street.
He is avoiding all contact with colleagues by shutting himself away inside Number 11, where he lives. In a video posted on social media on Friday, he said: “I am working from home. I’m self-isolating. And that’s entirely the right thing to do.
“But be in no doubt that I can continue, thanks to the wizardry of modern technology, to communicate with all my top team to lead the national fightback against coronavirus.”
Mr Johnson faced questions about whether he had ignored his own rules on social distancing, as he, Mr Hancock and Prof Whitty all attended a Cabinet meeting on Tuesday, despite their crucial roles, when all other ministers dialled in.
There are now fears the virus could spread through the Cabinet as the three have had so much contact with ministers. Other Cabinet members will not, however, be tested unless they develop symptoms, because the Government is no longer tracing contacts of people who have the virus.
That means ministers face an anxious wait to find out whether they have been infected. A Downing Street spokesman insisted the three had not infected each other at the Cabinet meeting, or when Mr Whitty examined the Prime Minister, because it takes five days for symptoms to show after someone has caught the virus.
Mr Johnson tested positive late on Thursday after suffering symptoms earlier in the day. He took part in the Clap for Carers event without warning Mr Sunak that he was suffering the symptoms, but Number 10 said he had stayed more than two metres away from him at all times.
Mr Johnson’s fiancée, Carrie Symonds, who is pregnant, is understood to have been living away for at least a week as a precaution after several members of staff had to self-isolate after feeling unwell.
The Prime Minister chaired a meeting of the daily Covid-19 committee from his office on Friday morning despite suffering a temperature and cough, the two most common symptoms of the virus. He also took a call from the US President, Donald Trump, who wished him a “speedy recovery” as they discussed the international response to the pandemic.
If Mr Johnson becomes too ill to continue working, Dominic Raab, the Foreign Secretary, will become caretaker Prime Minister. Michael Gove, the Chancellor of the Duchy of Lancaster, said the Prime Minister’s illness was proof that “the virus doesn’t discriminate”.
Mr Hancock and Mr Whitty were also working from home on Friday. No other Cabinet ministers have so far tested positive, but one minister said: “Between them, they have seen every single Cabinet minister in the last 10 days. It’s going to go through all of us.”
Mr Johnson attended Prime Minister’s Questions in Parliament on Wednesday and came into contact with several other ministers and MPs as well as the Speaker, Sir Lindsay Hoyle, 62, who said on Friday that he was in good health.
Downing Street said it was impossible to say from whom Mr Johnson had caught the virus, although numerous members of staff had gone home in recent days after falling ill.
Mr Hancock was the first to show symptoms, complaining of a sore throat on Wednesday afternoon. He was tested on the advice of the deputy chief medical officer and informed on Friday morning that he had the virus. He had been due at the daily press conference that afternoon, but was replaced by Mr Gove.
With Mr Johnson self-isolating at Number 11, the doors to Number 10 and Number 12 have been shut and his meals and red boxes are being left outside his office by staff who knock and then retreat.
Sir Mark Sedwill, the Cabinet Secretary, the fourth person to attend Tuesday’s Cabinet meeting in person, was said on Friday to have no symptoms.