The UK Government’s proposed drastic action, involving millions of people staying at home, should keep the number of deaths from coronavirus below 20,000, its Chief Scientific Advisor has told MPs.

Sir Patrick Valance suggested this would be a “good outcome” and claimed the latest measures should begin to produce results after about two to three weeks with the number of new cases starting to fall.

He told the Commons Health Committee case isolation could bring the peak of the outbreak down by about 20 per cent, whole household quarantine by about 25 per cent, and general social distancing by about 50 per cent. Social "shielding" of the elderly could reduce the mortality rate by between 20 and 30 per cent.

"Together you should expect those to have a very significant effect on the peak and we should start to see the rates come down in two or three weeks’ time," explained Sir Patrick.

He then told MPs the hope was to keep the number of deaths below 20,000.

"That is the hope that we can get it down to that. To put that into perspective, every year in seasonal flu the number of deaths is thought to be 8,000.

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"If we can get this down to numbers 20,000 and below that is a good outcome in terms of where we would hope to get to with this outbreak. It is still horrible. That is still an enormous number of deaths," admitted the CSA.

He suggested there could be as many as 55,000 coronavirus cases already in the UK.

Jeremy Hunt, the former Health Secretary who now chairs the committee, asked whether the expected death rate was one fatality for every 1,000 cases, which would mean that there were "potentially 55,000 cases" at present.

Asked if that felt right, Sir Patrick replied: "We've tried to get a handle on that in Sage [the Government’s scientific advisory group for emergencies] and if you put all the modelling information together, that's a reasonable ballpark way of looking at it. It's not more accurate than that."

Sir Patrick called for a "big increase" in the amount of testing that is done for the virus.

Asked if testing on the scale of South Korea was required, the CSA said: "We need a big increase in testing. That's what I'm pushing for very hard. Everyone is working hard to try and make that happen."

But Sir Patrick said it was important not to have people turning up to hospitals for tests and instead a community-based approach was needed, possibly involving the private sector.

"There is a lot of work going on in Public Health England, NHS and the Department for Health and Social Care to select which test we should go for and how that can be ramped up - possibly, and I think quite rightly - by the private sector, so we can get things out there fast on the community side, having the other parts of the testing controlled by Public Health England for the hospitals and the other bits that need to be done."

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The CSA said closing schools remained an option that was on the table to curb the spread of coronavirus.

He told MPs closing schools "would have an effect" but less so than other interventions and "it has all sorts of complicated effects as well", including potentially leading to children being looked after by grandparents.

It would also cause an "enormous problem" for the workforce, including in the NHS.

"It's absolutely on the table, as the whole suite of measures are, the evidence base is there to suggest where it might work and where it doesn't work, and decisions will, I'm sure, be made at the time they need to be made around school closures, which is one of the levers to pull to try to get on top of this at the right time. But it's not without quite complex consequences."

The number of people to test positive for coronavirus in the UK as of 9am on Tuesday was 1,950, up 407 or 27 per cent from 1,543 on Monday.

A total of 50,442 people have been tested with 48,492 negative results.

The department said an update on the number of deaths would be announced later today. The total is currently 55.