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The army will be put on standby, schools could be closed for three months and police told to focus only on serious crime under Boris Johnson’s doomsday plan to tackle coronavirus in the UK.

A new government battleplan published on Tuesday also predicts that up to one fifth of Britain’s working population – six million people – may be “absent from work” during the peak of the outbreak this summer.

Among the emergency measures being drafted are:

• Advising people to work from home where possible
• Cancellation of all non-urgent NHS treatment
• Police focusing on core functions like maintaining public order
• The armed forces replacing police at key sites such as nuclear power stations
• Helping firms to avoid cash flow by giving them longer to pay tax

Speaking at a press conference in Downing Street, the prime minister said he was confident the British public and the NHS would rise to the ‘national challenge’ posed by the disease.

Johnson and his chief medical and scientific advisers said that the immediate aim was to delay the widespread outbreak of the virus until the summer, when hospitals would be better able to cope.

But once the outbreak was established, the priority would be to spend three months using emergency powers to limit the risk to public health, with pensioners and those with underlying health conditions most at risk.

Johnson said that for most people who contract the virus it would be a “mild disease from which they will speedily and fully recover”.

England’s chief medical officer, Chris Whitty, told reporters “probably around 1% of people who get this virus might end up dying”, but stressed that 99% would not.

He said the the death rate varies according to age group – with older people more vulnerable.

And Whitty was keen to point out that the “great majority” survive coronavirus, even among the elderly.

The wargaming will involve deploying the Army to key sites, including nuclear installations, to help relieve the pressure on the police.

The PM said the police will “prioritise” their approach to maintaining order and serious crime, adding “the Army is of course always ready to back-fill as and when, but that is under the reasonable worst case scenario.”

In a bid to calm fears of a lack of mortuary space for any deaths, the government’s plan hopes to ensure “dignified treatment of all affected including those who die”.

Pensioners, who are most at risk from the disease, could also be advised to stay away from public events like the VE Day celebrations due on May 8.

Johnson confirmed for the first time that Matt Hancock, the health secretary, has also held talks with social media companies in order to prevent the spread of disinformation.

Sir Patrick Vallance, the chief scientific adviser, said there was “absolutely no reason to panic-buy or keep large supplies of everything”.

And he stressed that the public should not cancel summer holidays because by then the whole world would be likely to be beyond the point where travel would make a difference to transmission of the disease.

After an expected nine-week delay phase ends in May, the raft of “reasonable worst case (RWC) scenario” measures is likely to be needed for 12-weeks from May to the end of July.

But moves to cancel large-scale public gatherings such as football matches may not be needed given that the virus is more likely to be caught in groups of 12 rather than 40,000.

The elderly and those with underlying health conditions are most at risk from Covid-19 and are likely to be advised to stay away from public gatherings.

The 75th anniversary of VE Day takes place on May 8, just at the start of what could be the peak of the outbreak in the UK.

A special plan to help care homes for the elderly to maintain supplies of food and medicines is also being drafted.

School closures are still being weighed up as government health and science advisers are balancing the impact on their education compared to the health benefits. Singapore has not closed its schools but Japan has done so for a whole month.

Although some public health officials and Mayor of London Sadiq Khan have stopped shaking hands, Johnson revealed that he was continuing his own practice of handshaking.

“I am shaking hands, I was at a hospital the other night where I think there were coronavirus patients and I was shaking hands with everybody, you will be pleased to know, and I continue to shake hands,” he said.

“People must make up their own minds but I think the scientific evidence is… our judgment is that washing your hands is the crucial thing.”

Amid fears that workers could lose out financially, the PM added that he was “going to keep all options under review” on getting employers to pay out statutory sick pay.

Emergency legislation, likely to come before parliament later this month, is expected to include new time-limited plans to relax rules to allow bigger class sizes and for pupils to transfer to different schools.

Moves to quarantine and test overseas visitors are also under consideration.

The government has said people should also check Foreign Office advice before travelling abroad and be understanding of the pressures the health service is under.

The 2020 Tokyo Olympic Games, set to open on July 24, could be postponed until the end of the year.

The viral outbreak of Covid-19, which began in China, and has infected more than 80,000 people and killed more than 2,700 globally.