Mr Johnson has tested positive for coronavirus, Downing Street says. His symptoms are mild and he will continue to lead the government response to the virus while he self-isolates, a spokesman says.
Mr Johnson own words:
"I've developed mild symptoms of the coronavirus, that's a temperature and a persistent cough," Mr Johnson said in a video posted on his Twitter account.
"On the advice of the chief medical officer, I have taken a test and that has come out positive.
"I'm working from home and self-isolating. That's entirely the right thing to do.
"I can continue, thanks to the wizardry of technology, to communicate with my top team and lead the national fightback against the virus."