The Prime Minister has been suffering with coronavirus for eleven days now and was admitted to hospital on Sunday night.
This evening Downing Street confirmed Mr Johnson has been moved to an intensive care unit.
The markets have responded to the announcement with the value of the pound plummeting against the US dollar.
At 6.50pm the pound was valued at $ 1.23093 however it has since dropped to $ 1.1.22416.
More to follow…
A Number 10 spokesman said: “Since Sunday evening, the Prime Minister has been under the care of doctors at St Thomas’ Hospital, in London, after being admitted with persistent symptoms of coronavirus.
“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 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.”