The British army is ready to support police in maintaining public order as part of government planning for the worst-case scenario spread of coronavirus, Prime Minister Boris Johnson said on Tuesday.

The government published its "battle plan" for tackling the spread of coronavirus on Tuesday, including possible school closures and home working, as it warned as many as one-fifth of employees could be absent from work during peak weeks.

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Asked during a media conference about the possibility of drafting in the army if the police force is struck by staff shortages, Johnson said: "The army is of course always ready to backfill as and when, but that is under a reasonable worst-case scenario."

But it seems unlikely Britain - which has 39 known cases at time of publication - will lock down any cities to prevent the spread of coronavirus. The government will, however, keep all options available, England's Chief Medical Officer Chris Whitty said on Tuesday.

"Locking down a city is most useful when it is starting in one place with a high transmission in that place and nowhere else," Whitty said at a media conference alongside Johnson.

"It seems unlikely we will be in that situation in the medium to long-term future, but it is important that all the options are available to people."

Four-stage plan

The coronavirus outbreak could also cause the police to drop low-priority cases and force the NHS to delay non-urgent care, according to the government's plan.

The 27-page document sets out the UK-wide response to COVID-19 amid widespread concerns about the impact the virus will have on people's wellbeing, the economy and public services.

Measures aimed at delaying the spread of the virus could include school closures, "reducing the number of large-scale gatherings" and encouraging greater home working.

The government's response comes in four stages: containing the outbreak, delaying its spread and mitigating the impact of the disease once it becomes established, and alongside that, a research programme is aimed at improving diagnostics and treatment for the disease.

Launching the plan at Downing Street, Johnson said he had "no doubt at all" that the "country is going to get through coronavirus, and get through it in good shape".

But he stressed it was "highly likely" the number of coronavirus cases in the UK would rise.

"Let me be absolutely clear, that for the overwhelming majority of people who contract the virus, this will be a mild disease from which they will speedily and fully recover, as we have already seen.

"But I fully understand public concern, your concern, about the global spread of the virus and it is highly likely that we will see a growing number of UK cases, and that's why keeping the country safe is the government's overriding priority, and our plan means we are committed to doing everything possible, based on the advice of our world-leading scientific experts, to prepare for all eventualities."

Amid warnings about the impact on the global economy, and with Chancellor Rishi Sunak forced to draw up plans in his Budget to counter the disease, the document acknowledges the potential impact on businesses:

"In a stretching scenario, it is possible that up to one-fifth of employees may be absent from work during peak weeks."

Right now, as long as you wash your hands more often, that is the number one thing you can do to keep you and the country safe Matt Hancock, UK Health Secretary

The government's response is currently in the containment phase, along with research being carried out and planning for the delay and mitigation work.

Officials hope to delay the peak of the virus until the warmer spring and summer months when health services are less busy.

In a sign the military could be called in to help with the efforts, the document said there were "well-practised arrangements for defence to provide support to civil authorities if requested".

'War room'

The strategy also includes a "war room" to bring together communications experts and scientists from across government and the NHS to roll out a public information campaign.

Legislation allowing the government to use extra powers to help control COVID-19 is expected to go through Parliament by the end of the month.

Health Secretary Matt Hancock said on Tuesday the number of home ventilation kits is being expanded as part of an effort to keep people out of hospitals.

He told ITV's Good Morning Britain: "A lot of people, not least because it is mild, will be best off at home than in hospital, so we are expanding the number of home ventilation kits that are available so that can be done.

"The NHS, of course, has a full plan for this and prepares for this even when there isn't an outbreak."

Hancock told BBC Breakfast: "It's quite unusual for a government to publish a plan with things in it we hope we won't have to do."

Asked about the cancellation of mass gatherings such as the London Marathon at the end of April, Hancock said: "It's far too early to be able to tell in that instance. What we can say for sure is that, right now, we do not recommend the cancelling of mass events, and schools as well should not be closing unless there is both a positive case and the school has had the advice to close from Public Health England.

"So, right now, as long as you wash your hands more often, that is the number one thing you can do to keep you and the country safe."

Hancock said he understood why people may not want to shake hands, but added: "The scientific advice is that the impact of shaking hands is negligible and what really matters is that you wash your hands more often."