Since Sunday evening, the Prime Minister has been in St Thomas’ Hospital, in London.
A spokesperson for No.10 said: “The condition of the Prime Minister has worsened and, on the advice of his medical team, he has been moved to the Intensive Care Unit at the hospital.
“The PM has asked Foreign Secretary Dominic Raab, who is the First Secretary of State, to deputise for him where necessary.
“The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication.”
Cabinet Secretary Michael Gove is now also self-isolating after a member of his family developed coronavirus symptoms.
Gove is himself well and has no symptoms, but is staying at home and isolating for the time being.
Gove did a round of broadcasts from his home this morning, instead of going into the studios.