Health Secretary Matt Hancock is self-isolating after he tested positive for coronavirus.
The news comes as the Prime Minister Boris Johnson has also confirmed he has the virus.
The pair, who are leading the country's response to the Covid-19 outbreak, both said they have mild symptoms and are continuing to work from their homes.
In a video posted on Twitter, Mr Hancock said: "I've been working from home over the last couple of days, because everybody who can work from home should work from home.
"I've also had some mild symptoms and upon medical advice I was tested and that's been positive.
"I will be self-isolating until next Thursday.
"Fortunately for me, symptoms so far are very mild and I've been able to carry on working, driving forward the UK's response.
"I'd like to say a massive thank you to everybody in the NHS and social care right across the board on the response."
Downing Street said the advice on social distancing had been observed in Number 10.
A spokesman for the Chancellor of the Exchequer said Rishi Sunak has not had any symptoms and therefore has not been tested for coronavirus and is not self-isolating.
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