The Prime Minister spent the night in intensive care at a London hospital after his coronavirus symptoms worsened, but Downing Street said that he was receiving “excellent care”.

Boris Johnson was admitted to St Thomas’ Hospital on Sunday with persistent symptoms, nine days after it was revealed he had tested positive for Covid-19.

But the Prime Minister’s condition worsened on Monday afternoon – he was given oxygen before being taken to intensive care.

A Downing Street statement said: “Over the course of [Monday] 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 is receiving excellent care, and thanks all NHS staff for their hard work and dedication.”

Foreign Secretary Dominic Raab has been asked by Mr Johnson to deputise for him “where necessary”, while Buckingham Palace said the Queen has been kept informed of the Prime Minister’s condition.

Derek Hill, professor of medical imaging at University College London (UCL), said the PM could be given a breathing aid known as continuous positive airway pressure (CPAP), which bridges the gap between an oxygen mask and full ventilation.

CPAP uses pressure to send a blend of air and oxygen into the mouth at a steady rate, thereby boosting the amount of oxygen that enters the lungs.

READ MORE: Key questions after Boris Johnson moved to intensive careBut Professor Hill said many Covid-19 patients eventually “progress to invasive ventilation”.

This is for people whose illness is so severe they are struggling or unable to breathe for themselves.

A mechanical ventilator either does all the breathing for the patient, or assists the patient’s own breathing.

The patient is heavily sedated while a device called an endotracheal tube (ET) is guided through the mouth into the windpipe.

Heavy sedation is then continued because having a tube in the throat can be very uncomfortable.

Patients can be fed at the same time through a tube going into their stomach via their nose.

Prof Hill said it was unclear whether Mr Johnson was breathing on his own, or with the help of a ventilator.

He added: “One of the features of Covid-19 in all countries seems to be that many more men become seriously ill than women - especially in the over 40 age group.

“Also we know that people under about 60 seem to have a higher chance of making a recovery from critical illness with Covid-19 than older people.

“But there is no doubt this turn of events means Boris Johnson is extremely sick.