Questions remain over the UK's coronavirus strategy in the absence of Boris Johnson as the Prime Minister was spending a second night in intensive care.

And Britain has asked the US for 200 ventilators to fight the coronavirus pandemic, US President Donald Trump has said.

Some of the 4,000 beds in the new NHS Nightingale hospital have been taken up by Covid-19 patients as the coronavirus crisis deepens.

And the NHS has launched a mental health hotline to offer support to hundreds of thousands of health workers on the frontline in the fight against coronavirus.

As the pandemic grows, Dr Thomas House, a mathematical epidemiologist and one of the scientists advising the government during the current coronavirus crisis, has revealed all we know - and what we don't - about the crisis.

He told the Manchester Evening News : "It's a viral pathogen which colonises your respiratory tract and lungs. It's spread from person to person.

"It's one of the big challenges that our generation of humans has got to deal with."

On what started the pandemic, he admits: "We don't know. We have to wait for the genetics and science to come in.

"The theory about it starting in a lab doesn't seem terribly likely.

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"But the idea it emerged somewhere other than Wuhan and that's just where it got going in the human population is plausible. We just don't know where.

"You can do calculations with genetics and try and work it out. The fact we first saw a case in Wuhan doesn't mean that's the starting point."

On the need to socially distance, he adds: "Because we know it's spread directly from person to person and we don't have a medical intervention. For flu we have a vaccination but we don't have anything that works for coronavirus.

"There was a lot of clamouring to do it really early. But there was no point because there weren't enough cases for all the trouble it would have caused.

"By the time it was in lots of countries there was no chance of driving it to extinction like we did with SARS so you have to time it right so you're actually keeping people away from others who are infectious.

"Maybe it should have been a little earlier or a little later - but that's the kind of thing we can look back on. The strategy of not jumping straight away is correct.

"However the 'take it on the chin' idea was not right and was never what scientists were saying. Lockdown was necessary."

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On when the lockdown will be lifted, he continued: "We have to look at the figures in the coming days.

"We are going to have to come up with strategies for measuring the trade-off between the lockdown and the human cost and the economy. People are already finding it hard just a few weeks in.

"In a week's time we will have better knowledge of how much of an effect the current lockdown has had. We'll be able to look at hospital capacity."

What about these daily infection and death toll figures? "The fact they are shooting up doesn't mean social distancing isn't working, there's just a delay," he adds.

"It's the infections we are stopping now that will stop the future deaths

"It should start to decrease in the next week or two."

He adds: "Every year in the UK about 600,000 people die. If we just let the epidemic sweep through we might be thinking about doubling that.

"If we socially distance and ensure all the people who need treatment get treatment and don't overwhelm the NHS we can get that down.

"But I think even in the best case scenario, excess deaths will still be in the high tens of thousands or hundreds of thousands this year as a result of coronavirus - and there's the general disruption it's caused to medical care."

A lot of people feel angry that Governments - including the UK Government - weren't as prepared for a pandemic as it could have been. Do you think that's justified?

He says: "The scientific community has been saying 'get ready for this' for years. It's not just our Government - I've got lots of friends around Europe saying 'why weren't we more ready?'

"It think it's a problem that emergency preparedness seems like a natural thing to cut when you need to make savings.

"It costs money but it's worth it.

"It's so difficult because as scientists it's our duty to tell people the inconvenient truth. This is something we are in for the long-haul.

"People should be ready for that.

"Coronavirus will be one of the main things humans die of this year. But we live in a safe society where most people don't die in a given year.

"Worry is never helpful but people should care about it enough to modify their behaviour.

"Car accidents are another big cause of death in this country. When you get in a car worry isn't helpful. But you should recognise the risks and put on a seatbelt and not drive recklessly. In the same way people should obey self-distancing and be hygenic.

"It's a real thing and people should modify their behaviour to address that.

"But don't despair because this is something we can do something about.

"It's not like this scary thing happening that we can't control. We can all pull together and get through it.

"For example, a thousand scientists have volunteered to help with coronavirus research in this country."

On the best case scenario, he says: "A vaccine that comes very quickly."

And if not? "Second best is we manage the epidemic well, the NHS doesn't get overwhelmed, and it spreads in the way coronavirus viruses usually do," he says.

"In films the virus always evolves to be more scary, actually evolution works the other way. It tends to make them less deadly.

"We've seen very young people are not in as much in danger. If there's something circulating the whole time, immune system gets better at dealing with it.

"The antibody test will give crucial information on how many people just get a mild cold.

"Humans have been through big pandemics before right through history.

"The worst was 1918. There were a few in the 19th century, three in the 20th century. We were lucky with SARS and Ebola and MERS that they were contained.

"If we don't get an effective vaccine there are probably going to have to be a lot of infections with this disease.

"Herd immunity shouldn't have been the main strategy. But we have to manage the acquisition of that while giving as much time as possible.

"Once we get the antibody tests we'll know more about how close to herd immunity we are.

"I think some people may think just stay home for a few weeks and that's that - but it's longer haul than that.

" There will be consequences for the rest of 2020. But we'll get better at managing social distancing and work out which activities cause the least disruption for most benefit.

"The sort of thing that might change is if we see evidence that it's not good at spreading outdoors then we might have a policy of people being able to go outdoors.

"There might be less worry about parks, for example. Hopefully we will get better at managing activities and which ones are safe and which aren't.

"In terms of some measures like increased hygiene and thinking about being careful with transmission, that's going to carry on throughout 2020.

"We'll have to be aware of it for the rest of the year.

"After that it will depend on how long people have immunity."

On face masks, he says: "There's really good guidance from WHO that came out that said basically even if masks help if you buy them in the current circumstances you are keeping them away from health workers.

"But I think we might want to look at whether mask-wearing is a good habit to pick up during future pandemics. Also most people don't know how to wear them to protect themselves properly.

"Nobody can look at what's happened and not appreciate the NHS and other key workers. I'm pretty sure everyone will think about how we are looking after these people who do crucial jobs."

"I think by 2021 the hope is coronavirus will just be seasonal like other viruses," he added. "Humans have got through pandemics before and we will get through this."