The coronavirus outbreak at the heart of the UK government spread on Monday with Prime Minister Boris Johnson's senior adviser, Dominic Cummings, self-isolating with symptoms just days after the British leader himself tested positive.
A Downing Street spokesman said Cummings, one of the most powerful men in the government, had developed symptoms of COVID-19 over the weekend.
Johnson on Friday became the first leader of a major world power to announce he had tested positive for the virus. His health minister, Matt Hancock, also tested positive and the government's chief medical adviser, Chris Whitty, is self-isolating.
Cummings was seen sprinting out of Downing Street shortly after Johnson revealed he had tested positive. Last week, the adviser denied a newspaper report which said he had prioritized herd immunity and the economy in the coronavirus crisis at the expense of pensioners dying.
Britain initially took a modest approach to containing the spread of the disease compared to its European peers such as Italy and France.
But Johnson imposed stringent controls after projections showed a quarter of a million people could die. He is now self-isolating in Downing Street.
Scientists say the virus's incubation period is estimated at between one and 14 days, and there have been anecdotal accounts of people spreading the disease without having symptoms.
Besides meetings in Downing Street, Johnson ventured beyond Downing Street last week. On Wednesday, a day before his positive test, Johnson answered questions at a weekly session in parliament's House of Commons chamber.
Johnson also spoke with several lawmakers. Minister for Scotland Alister Jack, who sat next to Johnson before the session, said on Saturday he had developed a temperature and a cough and was now working from home in isolation.
Health officials said on Sunday that figures showed that 1,228 patients in the UK who tested positive for coronavirus (COVID-19) had died.
As of 0800 GMT on March 29, a total of 127,737 people in the UK have been tested, of which 108,215 were confirmed negative and 19,522 were confirmed positive.