Britons should get ready for "changes to our way of life and what our country looks like" - lasting from the end of March until the summer and "perhaps a lot longer" - senior ministers have warned, as they prepared for a dramatic escalation of the coronavirus crisis.
With the UK heading towards what the chief government scientist says will be "the start of the peak" of the outbreak later this month, BuzzFeed News can reveal:
Measures put in place until around the start of April, such as encouraging working from home and the postponement of sporting fixtures, will likely have to be extended until the summer.
Travel abroad will become extremely difficult from next month, ministers believe, potentially causing the cancellation of hundreds of thousands of holidays - but Downing Street is privately scathing about Donald Trump's travel ban.
Ministers are urging Boris Johnson to pass legislation that will radically extend the government's emergency powers capabilities beyond the current 30 day time-limit.
One senior minister admitted that the prime minister could be forced to delay the Brexit transition period and said the UK was "almost certain" to enter recession.
Ministers are considering proposals to suspend competition law for supermarkets and waive carrier bag charges, and even use the armed forces to deliver food to shops, with students and other volunteers enlisted for a national campaign to help the elderly and vulnerable.
Downing Street's response to what Johnson has called "the worst public health crisis for a generation" will define his premiership, his allies said.
But as Number 10 prepared stricter measures to stop various types of public events, including mass gatherings, beginning next week, some in Whitehall expressed concerns that there is no scientific consensus on whether the UK's so-called "herd immunity" and "flatten the peak" strategies will work.
So far, the UK government has imposed less stringent measures on the public than some other European countries - several of which have closed schools and borders - with Number 10 insisting it is being "guided by the scientific advice" from its chief medical officer Chris Whitty and chief scientific adviser Patrick Vallance.
But as the "peak" of the coronavirus outbreak in the UK begins at the end of March, Britons should expect a series of tougher new measures bringing unprecedented disruption to their daily lives, ministers and aides told BuzzFeed News.
At present, the corporate advice from some companies on whether employees should work from home and restrict their movements has gone beyond the official government instructions. Many firms - including BuzzFeed - have told staff to work from home, and some have also advised employees to avoid public transport and crowded places until the end of the month. The English Premier League has postponed all fixtures until April 4.
From April, that will become the norm for millions of workers across the country, a government source said, warning it was likely that many more companies would take similar measures and that home-working would continue until June at the earliest.
The government is escalating its own official advice next week, including introducing versions of some measures that it has previously rejected, such as restrictions on mass gatherings. The priority for the government will be measures aimed at ensuring the safety of elderly and vulnerable people.
It is difficult to see how football fans will be able to return to stadiums in April and May or how the Tokyo Olympics will be able to go ahead, the government source added.
International travel is also likely to become much harder from next month, senior ministers believe, with the Foreign Office limiting travel to more and more countries affected by coronavirus, air travel companies cancelling flights and other nations imposing blanket, unpredictable restrictions on who can cross into their borders.
On Friday, the FCO updated its travel advice to advise against all but essential travel to much of Spain. Denmark closed its borders on Saturday and Poland is following suit on Sunday.
Ministers are preparing contingency plans for the insurance industry's response to potentially hundreds of thousands of people who will have to cancel their holidays.
While Downing Street publicly insisted on Friday that it will not delay the UK's transition period with the EU, a minister told BuzzFeed News that in truth "nothing can be ruled in or out", leaving the door open to the prospect of Britain maintaining its standstill arrangement with Brussels beyond the end of the year. On Friday, BuzzFeed News revealed that plans to hold some negotiations via video conference could be scuppered by the outbreak too.
The minister also said that the UK was "almost certain" to enter into a recession as the economy is impacted by the virus.
Some ministers are urging Johnson to pass legislation that will dramatically extend the emergency powers available to the government.
The Civil Contingencies Act currently limits the use of emergency powers - which include suspending the rule of law and deploying the army, banning public assembly and imposing travel restrictions - to 30 days.
But ministers are worried that, if parliament is shut down by the virus, the 30 day expiration date will not be sufficient and that the government should have emergency powers at its disposal for a longer period. This is likely to prove highly controversial with opposition parties.
Number 10's priority in tackling the coronavirus has been to ensure that the NHS is in the best possible position to cope when the number of people requiring treatment reaches its peak - expected to be around May.
Yet there are concerns among the government's medical experts that, if their plan to delay and spread out the peak of the epidemic is unsuccessful, and there is a sharp spike in cases instead, the NHS will not be able to provide enough hospital beds or ventilators for people who need them.
In this worst-case scenario, the death toll is expected to rise significantly beyond the 100,000 figure reported by the Sunday Times last weekend.
Publicly, the government has remained united in its support for Whitty and Vallance's expert advice - and there is consensus among Johnson and his closest aides that they have taken the correct approach.
Privately, some ministers and Tory MPs have told BuzzFeed News that they think the government should have taken further steps to prevent the spread of the virus immediately.
One minister said there is no scientific consensus on what is the right thing to do. A Tory MP said that Johnson faces a "political shitstorm" if the UK is affected worse than other countries and that he will not be able to use Whitty and Vallance as "human shields".
But other members of the government defended the government's "herd immunity" approach to BuzzFeed News - the theory detailed by Vallance on Friday that allowing the virus to spread to around 60% of the population, while protecting the elderly and vulnerable, is the best way to build immunity and fight it in the long-term.
Not doing so, one government source said, would lead to a second wave of the outbreak next winter that would end up being far more deadly, according to the expert advice. Everything the government is doing is about preventing that worst-case outcome next winter, the source said, insisting that their reasoning was based on epidemiological science and not behavioural science.
Downing Street is internally scathing at the approach taken by Donald Trump - who suspended travel from most of Europe to the US last week - believing it is an irresponsible measure based on anti-immigrant politics rather than science, since the virus is already widespread throughout America. The UK's strategy is far more similar to that of Germany and France than the US, the government source said. On Friday, Trump claimed that European countries were "calling us, asking for advice".
Johnson's allies also accept that they have had difficulty communicating the UK's strategy to the public.
They believe the press conferences with Whitty and Vallance are authoritative and helpful in explaining the situation to the media, but are concerned the wider public properly comprehends neither the herd immunity approach, nor how it should be responding to the outbreak. People are either not taking it seriously enough or panicking and resorting to things like stockpiling, a source said.
One particular area of frustration is the NHS 111 phone service, which the public can call for advice on what to do if they think they have coronavirus. The service is severely underperforming, Whitehall officials believe, and Downing Street is exploring how the public can better receive healthcare advice, including potentially via private tech companies.
Other proposals under consideration by ministers include extraordinary measures to help supermarkets remain stocked and able to deliver food to the elderly.
Ministers are looking at possibly suspending competition law to allow supermarkets to share data so they can coordinate deliveries, as well as waiving the 5p carrier bag charge, because supermarkets believe customers bringing reusable bags into shops could spread the virus further. They are also looking at drafting in the armed forces to deliver food to shops.
Johnson also wants an army of sixth formers, students and other volunteers to take part in a national effort to protect the elderly and vulnerable.