After his coronavirus symptoms worsened, Prime Minister Boris Johnson spent the night in intensive care at a central London hospital.
Downing Street said he had been admitted to the unit on his medical team’s recommendation, and provided “excellent care.”
A spokesman added that Mr Johnson asked Foreign Secretary Dominic Raab to substitute “where necessary.”
The 55-year-old prime minister was admitted to St Thomas Hospital on Sunday evening, with “persistent symptoms.”
According to Buckingham Palace, the Queen was kept informed about the health of Mr Johnson by No 10.
World leaders have voiced their support for Mr Johnson, including US President Donald Trump and French President Emmanuel Macron.
A media source correspondent said the prime minister was given oxygen late on Monday afternoon, before he was admitted to intensive care.
He was moved as a precaution to be next to a ventilator-which takes over the body’s mechanism of breathing, said a local media source.