London (CNN) The UK's response to the coronavirus pandemic was upended on Friday when the Prime Minister Boris Johnson and his top health minister tested positive for the infection, and his chief medical adviser self-isolated after displaying symptoms.

Johnson announced his diagnosis in a remarkable video posted on social media, in which he said he would continue to lead the UK government's efforts from self-isolation in an apartment in Downing Street. Minutes later, his secretary of state for health, Matt Hancock, also said he had the virus and would work from home.

The Prime Minister said he'd been tested on the advice of England's chief medical officer, Chris Whitty. A matter of hours later, Whitty said he was going into self-isolation after displaying symptoms of Covid-19.

Over the last 24 hours I have developed mild symptoms and tested positive for coronavirus.



I am now self-isolating, but I will continue to lead the government's response via video-conference as we fight this virus.



Together we will beat this. #StayHomeSaveLives pic.twitter.com/9Te6aFP0Ri — Boris Johnson #StayHomeSaveLives (@BorisJohnson) March 27, 2020

The extraordinary developments raised the question of how many officials leading the UK's response to coronavirus had themselves been exposed to it. Downing Street, the center of power in the UK, is a maze of cramped offices and narrow corridors, making it almost impossible for everyone working there to practice the government's own advice on social distancing.

On Thursday evening, after displaying symptoms but before learning the result of his test, Johnson appeared outside 10 Downing Street with his chief finance minister, Rishi Sunak, taking part in a national moment of appreciation for the UK's health service workers. A Downing Street spokesperson said the pair were careful to remain at a safe distance.

Boris Johnson, right, taking part in a national applause with his chancellor, Rishi Sunak.

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