Health Secretary Sajid Javid has confirmed that he has contracted Covid-19 just over a day before lockdown restrictions are lifted in England.
Mr Javid said a full PCR test confirmed the result of an earlier lateral flow test that he was positive for the disease.
He said in a message posted on his Twitter feed: “My positive result has now been confirmed by PCR test, so I will continue to isolate and work from home.”
The result is the signal for NHS Test and Trace to begin tracking down his recent close contacts and instructing them to quarantine.
It could potentially mean a swathe of ministers and senior Whitehall officials will be confined to their homes when restrictions lift on so-called “freedom day”.
Downing Street would not comment on suggestions Boris Johnson could be among them after he was reported to have had a lengthy meeting with Mr Javid in No 10 on Friday.
The timing could hardly have been worse for Government with scientists voicing increasing concern at the idea of ending all statutory legal controls while cases continue to surge.
It raises the prospect that “freedom day” will descend into chaos with ministers reduced to welcoming the changes remotely from their living rooms.
The Liberal Democrats said that Mr Javid’s positive test underlined the case for Government to rethink its plans.
Health spokeswoman Munira Wilson said: “This shows no-one is safe from this deadly virus.
“By easing all restrictions with cases surging, they are experimenting with people’s lives.
“Right now, they are pursuing a strategy of survival of the fittest, where the young and clinically vulnerable will be left defenceless.”
Mr Johnson has repeatedly said he wants the lifting of lockdown to be “irreversible”, but in recent days ministers have begun to sound more cautious.
While social-distancing rules in England will come to an end, Government guidelines advise face masks should still be worn in enclosed spaces such as in shops and on public transport, while pubs and bars should be table service only.
Meanwhile the Government is facing calls from business to overhaul the NHS Covid app amid growing alarm at the numbers of staff missing work after being “pinged” and told to self-isolate.
The London Underground became the latest to succumb with the Metropolitan line forced to close on Saturday due to a shortage of control room staff.
Earlier Mr Javid said he had taken a lateral flow test on Saturday morning after feeling “a bit groggy” the evening before.
He said he had recorded the positive result, despite having had both doses of the vaccine, but was only experiencing “mild” symptoms.
His positive test meant that Communities Secretary Robert Jenrick had to be drafted in to replace him in a series of broadcast interviews with the Sunday morning politics shows.
Mr Javid was only appointed to the post last month following the resignation of Matt Hancock after CCTV footage emerged showing him kissing an aide in his office in breach of social distancing rules.
He is seen by Tory MPs impatient with lockdown measures as being noticeably keener than his predecessor on easing restrictions.
Meanwhile the Department of Health and Social Care (DHSC) insisted no decisions had been made after it was reported that ministers were set to come out against mass vaccinations for teenagers.
The Sunday Telegraph reported that guidance due to be issued on Monday was expected to recommend the vaccine is offered to vulnerable 12 to 15-year-olds and to 17-year-olds who are within three months of turning 18.
The paper said the Joint Committee on Vaccination and Immunisation (JCVI) is believed to have advised against the rollout of vaccines to all children until there is further evidence on the risks involved.
A DHSC spokesman said: “The Government will continue to be guided by the advice of the JCVI and no decisions have been made by ministers on whether people aged 12 to 17 should be routinely offered Covid-19 vaccines.”