Foreign Secretary Dominic Raab, speaking at a press conference at Downing Street, said the Prime Minister remained "under observation" in hospital following his admittance with coronavirus on Sunday.

"I can tell you the PM had a comfortable night in hospital and is in good spirits," said Mr Raab.

"He is still in hospital under observation. He is being given regular updates on developments and he continues to lead the Government."

Mr Raab gave an update on the number of people the Foreign Office has helped to return to Britain.

He told a press briefing that his department had helped 200,000 return on commercial flights from Spain alone since the crisis began, 13,000 from Egypt and 8,000 from Indonesia.

Chartered flights by the UK Government from seven countries had helped more than 2,000 British nationals return home, while another 1,500 had been repatriated from cruise ships.

And the Cabinet minister promised all was being done to return those still stuck abroad, with more flights from India, South Africa, Nepal and the Philippines flying in later this week.

Mr Raab reiterated that the Prime Minister was admitted to hospital "as a precaution only".

He said: "He was admitted to hospital for tests as a precaution only.

"And that was because some of the symptoms that he had when he first tested positive had persisted.

"He's had a comfortable night in St Thomas' (Hospital), he's in good spirits, and he's being regularly updated.

"And he still remains in charge of the Government and we are getting on with all of the various strands of work to make sure at home and abroad we can defeat the virus and pull the country through coronavirus and the challenges that undoubtedly we're facing at the moment."

Mr Raab praised those on the front line of fighting the coronavirus pandemic, following the Queen's tributes on Sunday to the "national spirit of unity and resolve".

He said: "From our heroic doctors, nurses and care workers, through to those manning the tills at supermarkets and pharmacies, to those driving the lorries and the buses, they are all worthy of our applause and they are all worthy of our admiration.

"And on that note, both the Prime Minister and I would like to thank all the NHS staff for their truly heroic work and we urge the public to continue to follow the Government advice to stay at home, protect the NHS and save lives."

Professor Dame Angela McLean, deputy chief scientific adviser, said the efforts by Britons to stay at home "are working", and said the growth in the number of Covid-19 cases in hospitals is "not as bad as it would have been if we had not made these efforts".

She said: "It is working but the big question is, is the virus spread slowing down enough to make hospital admissions stabilise and then even fall?"

Dame Angela said the hospital admissions data by region had risen "very steadily" until April 1 and then showed a "more complicated behaviour, starting we hope to slow down".

She added: "But it really is too soon to see the effects of the big changes we've all made to our lives from March 23 onwards because that's only two weeks ago and it takes several weeks after you've become infected for you to realise you're ill enough that you really need to be in hospital.

"We're all watching these numbers very, very carefully and we're very much hoping what's going to happen next is they will at least stop rising."

Mr Raab said that the Prime Minister's team are "full throttle" in making sure that his directions and instructions are being implemented whilst he is in hospital.

He said: "Look, he's (Mr Johnson) in charge, but he'll continue to take doctors' advice on what to do next."

He said the team was "full throttle making sure that his directions and his instructions are being implemented and followed through whether it's the purchase of ventilators through to the diplomatic effort to return UK nationals who are stranded abroad".

"But as ever, the Prime Minister will take the medical advice that he gets from his doctor."

Mr Raab said the Government's top priority is to "stop the spread and make sure we can get past the peak".

He was asked about what the Government's "exit strategy" is from the current lockdown policy.

He said: "That's the over-riding focus of the Government right now. The other decisions can be considered in light of the evidence that we're taking from Angela and Chris in due course."

Dame Angela said: "We need a good, long time series of data on all of these stages of infection in order to be able to tell what the impact of the measures that came on March 23 are going to be.

"It's too early to tell yet, we need people to carry on following those instructions so that we can work out three weeks later what actually happens in hospitals."

She added: "We need to know how well the current restrictions are working before we can say anything sensible about what the next stage might be."

Professor Chris Whitty, in his first public appearance since recovering from coronavirus symptoms, said that it would be a mistake to discuss the next phase of managing the pandemic until there is confidence that the peak has been reached.

He said: "The key thing is to get to the point where we are confident we have reached the peak and this is now beyond the peak and at that point I think it is possible to have a serious discussion about all the things we need to do step-by-step to move to the next phase of managing this.

"But I think to start having that discussion until we're confident that that's where we've got to, would I think be a mistake."

Prof Whitty said it was "critical" for the NHS to always have an excess of available critical care beds during the fight against coronavirus.

He told a press briefing: "Our principle aim... is to ensure the gap between the number beds available for intensive care and those that are needed is always in a situation where we have some room to spare.

"And if we end up in a situation where we have more ICU beds at all times during this epidemic than we absolutely need to deal with Covid and other areas, that will be a success.

"That is something which is critical for our overall aim. What we would like to see is some headroom between what we need and what we have available at any given time, both for Covid and other conditions."

Mr Raab said the building of additional NHS Nightingale hospitals in areas such as Bristol, Harrogate and Birmingham was about ensuring there was a spread of critical care beds across England.

He added: "We are not remotely complacent. We are doing everything we can to make sure we not only have the capacity but also room for manoeuvre."

Asked if the PM was taking a risk by continuing to work, Mr Raab said: "Just to be clear, the PM - both in terms of going into St Thomas' yesterday - was taking the advice of doctors, so he's followed the doctors' advice there and, in terms of his recovery in the days ahead, will continue to do so."

On the lockdown exit strategy for the UK, he said: "The risk right now is if we take our focus off the strategy which is beginning to work, is that we won't get through the peak as fast as we need to, which is why it's perfectly legitimate to ask the question, but the Government's over-riding priority has got to be to keep up the work and the commitment that so many people have made to make sure that we maintain the social distancing, we stop the spread, we protect the NHS as we come through the peak."

Mr Raab said he would not comment on security matters when asked if he had taken over any of the Prime Minister's security responsibilities.

He said Mr Johnson was being "kept abreast" of developments.

Pressed again on why Mr Johnson is sick enough to be in hospital but well enough to be running the country, Mr Raab said: "That's something he will decide on the medical advice he's received from his doctor."

Professor Whitty said he was not responsible for recommending Mr Johnson went to hospital, and praised the PM's medical advisers as "outstanding".

Asked about the pneumonia risk to Mr Johnson, Prof Whitty said: "I'm absolutely not going to discuss any individual patient nor, to be clear, do I have all the details; nor should I as this is an issue between him and his medical advisers.

"I can give a general answer which is the clear majority of people who do end up going to hospital, they end up going into a general bed, they may or may not need oxygen and other things, and they don't need to go further than that."

Professor Whitty said antibody testing - to see if people have had the virus and recovered - will be more effective "later in the epidemic".

He said: "At this point in time we would expect quite a small proportion of the population has probably got antibodies.

"There's two reasons for that. There's the proportion actually infected and then there's a period of time between somebody getting an infection and antibodies being routinely detectable.

"And it depends which kind of antibody you're talking about how soon that is.

"Most of the labs that have looked at this would say 21 to 28 days would be the kind of timescale you'd be talking about.

"They do tend to be more effective later in the epidemic."

Responding to a question about whether Government measures could be eased in a staggered fashion by either region or by type of person, Mr Raab said: "Obviously we're very mindful of the challenges businesses are facing, small businesses, all employers and of course the workforce as well.

"But the risk is if we start taking our eye off the ball, of tackling the coronavirus, stopping the spread and getting through the peak, we risk delaying the point at which we could in the future take those decisions on easing restrictions.

"So it is really important right now to keep the over-riding focus on maintaining the discipline that we've had, keeping adherence to the guidelines that the Government has set out and making sure that we stop the spread of coronavirus."

Professor Whitty added: "So my advice to the Prime Minister was to take the medical advice of the excellent NHS doctors who are advising him and I'm sure he'll continue to do that.

"The only bit of advice I gave in addition to that was - as was widely reported - I did advise him to get tested in the first place because I thought that was prudent, but after that I didn't wish to muddle my role with him, I'm not his medical practitioner, I'm his adviser on wider issues."