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Experts are predicting that around 250,000 people in Britain will die as a result of the coronavirus outbreak unless the government takes hardline action to protect the public.

A report by Covid-19 specialists at the Imperial College, which has been advising ministers, said that even with the “social distancing” plans set out by the government, the health system will be “overwhelmed many times over”.

In its latest report, it said the only “viable strategy” is a Chinese-style policy of “suppression” involving the social distancing of the entire population.

It said such measures would need to be maintained potentially for 18 months or more until an effective vaccine became available.

“Even if all patients were able to be treated, we predict there would still be of the order of 250,000 deaths in GB,” it said.

The Imperial College report said it had only reached its conclusions in the last few days based on experience in Italy and the UK.

The stark warning came as Boris Johnson ratcheted up the response to the escalating coronavirus outbreak, urging everyone in the UK to stop non-essential contact or travel with others.

The prime minister urged people to work from home and avoid pubs, clubs and theatres as he held the first in a series of daily Downing Street press conferences.

“This advice about avoiding all social contact is particularly important for people over 70, for pregnant women and for those with some health conditions,” Johnson said.

He also told all those with a persistent cough or high temperature to self-isolate for 14 days, and for their families to join them in doing it. 

The government will also no longer support mass gatherings with emergency workers.

Mass gatherings are something “we are now moving emphatically away from,” Johnson said. 

Johnson said, by the weekend, groups particularly vulnerable to Covid-19 – over-70s with underlying conditions – will be asked to stay at home for 12 weeks to “ensure this period of shielding, this period of maximum protection coincides with the peak of the disease”.

Special guidance will be issued by the NHS for the 1.4 million people most at risk from the disease – including the elderly with underlying health conditions – on further measures they need to take to “shield” themselves from it.

However, the Imperial College report warned that even with such a dramatic closing down of normal life, the surge capacity limits of health systems of both the UK and the US – which is adopting similar measures – were likely to be “exceeded many times over”.

“In the most effective mitigation strategy examined, which leads to a single, relatively short epidemic (case isolation, household quarantine and social distancing of the elderly), the surge limits for both general ward and ICU (intensive care unit) beds would be exceeded by at least eight-fold under the more optimistic scenario for critical care requirements that we examined,” it said.

“In addition, even if all patients were able to be treated, we predict there would still be in the order of 250,000 deaths in GB, and 1.1-1.2 million in the US.”

The report said there was now no alternative but to move to a policy of total “suppression” involving the social distancing of the entire population, home isolation of cases and household quarantine of their family members.

Even then, it said that it was “not at all certain” that the strategy would succeed in the long term.

“The social and economic effects of the measures which are needed to achieve this policy goal will be profound,” it said.

“No public health intervention with such disruptive effects on society has been previously attempted for such a long duration of time. How populations and societies will respond remains unclear.”

In response, a government spokesman said that the recommendations put forward its Scientific Advisory Group for Emergencies (Sage) were in line with “best current evidence”.

“This is a very fast-moving situation. In order to give the most robust scientific advice Sage draws upon and considers a range of evidence and views to reach its recommendations,” the spokesman said.

“Part of this evidence includes the latest modelling data from a number of experts. All Sage recommendations are in line with the best current evidence. We will be publishing further evidence shortly.”