It took only four days to go from being asked to stay at home if you felt ill to a plea from the prime minister to put our lives on hold for weeks - perhaps months.

From next weekend the elderly, vulnerable, and pregnant women will be asked to retreat into their homes for 12 weeks.

There is already a huge step change in the government's response, driven the by changing evidence and modelling around the spread and severity of the COVID-19 disease.

"We've had to accelerate," is how one senior government figure privy to some of the planning decisions put it to me on Monday night.

"We thought we could put these social distancing measures off for another week and push the social shielding [the elderly and vulnerable being asking to stay at home for three months] back a week after that, but we've had to bring it forward."


This is a global pandemic that now requires a wartime effort from all of us, with the UK now clearly on the same path as Italy, Spain, France as it begins to roll-out social lockdowns and home isolation.

More extreme measures - enforced curfews, school closures, travel bans - are all "under review".

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The step-change in the government's pace can be explained via a paper released on Monday night by researchers at Imperial College London, whose disease modelling has been feeding into the government's strategy on handling the virus.

In a nutshell, the change in pace and policy is designed to save more lives - perhaps a quarter of a million more lives - as the government shifts between the "mitigation model" - trying to slow the spread of the virus to the "suppression model" - trying to reverse the pandemic growth.

Image: One estimate puts the number of deaths under the old model at 250,000

The researchers at Imperial conclude in their paper that trying to slow the spread of the virus rather than trying to suppress the disease will overwhelm the NHS, with demand for intensive care beds exceeded eight times over and 250,000 deaths.

They have arrived at this conclusion in the last few days as they look to the likely demand for intensive care beds based on the experience of Italy - a country three weeks ahead of us on the curve.

The latest evidence suggests that 30% of patients admitted to hospital with COVID-19 will need critical care. Previous estimates were too low.

So we move this week from trying to slow the spread of the disease to trying to stop - or suppress - the spread.

The researchers at Imperial have concluded this is the "only viable strategy at the current time".

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But they also acknowledge it comes at a huge cost: "The social and economic effects of the measures which are needed to achieve this policy goal will be profound. Many countries have adopted such measures already, but even those countries at an earlier stage of their epidemic [such as the UK] will need to do so imminently."

With a raft of changes this week, there are still more to come.

Image: The COVID-19 crisis shows no sign of finishing any time soon

Draconian measures will save lives - perhaps over 250,000, according to Imperial's estimates.

But it will also have a profound impact on our communities and our economy.

Saving lives and stopping the transmission of the disease could mean that we all have to put our lives on hold for a year or even longer while we wait for a vaccine.

So when the prime minister described what is upon us as the biggest challenge we've faced as a nation since the Second World War, he was not exaggerating.

All the trade-offs are awful and the sacrifices required of all of us immense.