Johnson, who had gone into self-quarantine after testing positive for coronavirus last month and exhibiting "mild symptoms", was admitted to St Thomas' Hospital on Sunday evening.

"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," said a statement from 10 Downing Street, the BBC reported.

"The PM is receiving excellent care, and thanks all NHS staff for their hard work and dedication," it added.

Foreign Secretary Dominic Raab has been asked to deputise for the PM where necessary, the statement said