Prime Minister Boris Johnson has been moved to intensive care after his coronavirus symptoms have worsened.
The Prime Minister has asked Foreign Secretary Dominic Raab to deputise for him.
Mr Johnson, 55, was given oxygen late on Monday afternoon, before being taken to intensive care.
However, he has not been put on a ventilator.
A Number 10 spokesman said: “Over the course of this afternoon, 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 prime minister has asked Foreign Secretary Dominic Raab, who is the First Secretary of State, to deputise for him where necessary.
“The prime minister is receiving excellent care, and thanks all NHS staff for their hard work and dedication.”