Boris Johnson's chief adviser Dominic Cummings is self-isolating after experiencing symptoms in line with those of coronavirus.
The 48-year-old is said to have developed these over the weekend.
While self-isolating he is expected to keep in touch with Downing Street colleagues remotely.
Downing Street declined to comment on Mr Cummings's situation this morning.
As well as having been a prominent figure in Mr Johnson's team, Mr Cummings is also known for his role in the Vote Leave campaign ahead of the EU referendum.
His self-isolation comes just days after the Prime Minister, who is also working from home while isolating, confirmed he had been diagnosed with Covid-19.
Health Secretary Matt Hancock has also contracted the virus.
While Chief Medical Officer for England Chris Whitty is self-isolating due to symptoms, as is Scottish Secretary Alister Jack.
