Health Secretary Sajid Javid says he has tested positive for Covid-19 and is suffering “very mild” symptoms.
Mr Javid, who said he had received both vaccine doses, took a lateral flow test on Saturday morning after feeling a “bit groggy” on Friday night and it came back positive.
He said he is now self-isolating until he gets the results of a PCR test.
Meanwhile, England’s deputy chief medical officer, Prof Jonathan Van-Tam, has warned of a “bumpy winter” ahead.
It comes as the UK recorded more than 50,000 daily cases for the second day running, days before almost all legal restrictions on social contact are lifted in England on Monday.
There were 54,674 cases – following 51,870 new cases on Friday – with 41 deaths within 28 days of a positive coronavirus test.
The last time cases exceeded 50,000 was in mid-January.
In a video posted on his Twitter feed, Mr Javid said: “I was feeling a bit groggy last night, so I took a lateral flow test this morning and it’s come out positive, so I’m now self-isolating at home with my family until I get the results of a PCR test.
“I’m grateful that I’ve had two jabs of the vaccine and so far my symptoms are very mild.”
He urged people who had not been vaccinated yet to “get out there and get them as soon as you can”.
Mr Javid also said people who feel groggy or come into contact with someone who is positive should take a lateral flow test.
Mr Javid replaced Matt Hancock as health secretary less than three weeks ago after CCTV footage emerged showing his predecessor kissing a colleague in his office, in breach of social-distancing rules.
Mr Javid previously tweeted that he had received the Oxford-AstraZeneca vaccine.
A Public Health England study found two doses of the AstraZeneca vaccine was 60% effective at stopping symptomatic disease from the Delta variant, which is now dominant across the UK. Two jabs of the Pfizer vaccine was 88% effective.