Ministers and officials are waiting to find out if they will have to self-isolate after Health Secretary Sajid Javid tested positive for coronavirus.
It is understood Mr Javid had a meeting with the prime minister on Friday, hours before he started feeling unwell.
But as of late Saturday night, Boris Johnson had not been tracked down as a close contact by NHS Test and Trace.
Case numbers are continuing to rise ahead of the lifting of legal rules on social contact in England on Monday.
The health secretary, who has received both vaccine doses and described his symptoms as “very mild”, said he would continue to self-isolate and work from home.
He announced a PCR test had confirmed a positive result he received from a lateral flow test.
As a result, NHS staff will be looking at his recent close contacts – for example anyone he had been within 1-2m of for more than 15 minutes – and then order them to self-isolate as well.
According to BBC, Mr Javid was in Downing Street on Friday and there are now questions about who else may be forced into self-isolation.
He had been working from his office at the Department of Health and Social Care in Whitehall last week and was in the Commons chamber three times.
In November, Mr Johnson, six Conservative MPs and two political aides had to self isolate after an MP at a Downing Street breakfast meeting tested positive for Covid.
While social-distancing rules will end on 19 July, requirements to self-isolate will only be eased for fully vaccinated people four weeks later, and guidance will advise that face coverings should still be worn in enclosed spaces such as in shops and on public transport.
But the government is facing growing criticism over its plans.
There have been warnings that the UK may need to re-impose measures in the autumn with England’s deputy chief medical officer, Prof Jonathan Van-Tam suggesting a “bumpy winter” could lie ahead.
