Boris Johnson is self-isolating after meeting an MP who later tested positive for coronavirus.
The Prime Minister, who was admitted to intensive care with the virus in April, was told by NHS Test and Trace on Sunday to do so.
A Number 10 spokesman said Johnson is “well” and does not have any symptoms of Covid.
He was advised to self-isolate by test and trace after attending a 35-minute meeting with a small group of MPs in Downing Street on Thursday morning, including MP Lee Anderson.
Johnson tweeted on Sunday night: “Today I was notified by NHS Test and Trace that I must self-isolate as I have been in contact with someone who tested positive for COVID-19.
“I have no symptoms, but am following the rules and will be working from No10 as I continue to lead the government’s pandemic response.”
Johnson tested positive for Covid-19 at the end of March and was admitted to a London NHS hospital on April 5, which Downing Street said was a “precautionary step” as his symptoms persisted.
He then spent three nights in an intensive care unit, later revealing it “could have gone either way” and thanked NHS staff for saving his life.
A Number 10 spokesman said on Sunday: “The Prime Minister has today been notified by NHS Test and Trace that he is required to self-isolate as a contact of someone who has tested positive for Covid-19.
“The Prime Minister will follow the rules and is self-isolating.
“He will carry on working from Downing Street, including on leading the Government’s response to the coronavirus pandemic.
“The PM is well and does not have any symptoms of Covid-19.”