Significant further restrictions on our freedom to mix with people, in social or work settings, could be introduced in a fortnight, if the “rule of six” does not lead to behavioural change and a flattening of the coronavirus infection rate.
I have spoken to members of the government and to its scientific advisers, and am struck by how anxious they are that the virus may be spreading out of control again.
One member of the Scientific Advisory Group for Emergencies (SAGE) told me : “My big worry now is that we might be too late again to avert a major second wave.
"If we wait for deaths to go up again before taking decisive action we will be in trouble again”.
A senior member of the government told me he was acutely aware of the scientists’ concern.
“There is no possibility of us waiting for the death rate to rise before we act” he said.
He added the time frame for assessing whether this week’s new 'rule of six' had done enough to suppress the virus is a fortnight.
There is a view at the top of government that pretty much every social distancing measure should be contemplated other than school closures.
A leading scientific advisor told me: “Lockdown is the only thing that we know works, to be frank.
"I think that if we want to keep schools open, we probably have to give serious consideration to a wide range of other measures to stop a major second wave.
"And we have to think about doing that right now - which we are starting to do”.
Further restrictions on our way of life will split the governing Tory party.
Many Conservative MPs disapprove even of the new legally enforceable rule in England that we must never meet in groups of more than six and its variants in Scotland, Wales and Northern Ireland.
The prime minister has talked of a return to something like national lockdown as a “nuclear option”, a last resort.
But his and the Health Secretary Matt Hancock’s preference for targeted local action has been dealt a significant blow by the sudden overwhelming of the Covid-19 testing system by a surge in demand - which means it is now much more difficult for NHS Test and Trace to identify precisely where the virus is spreading.
Hancock faces a massive quandary in trying to match capacity more closely with those who need tests.
It will take weeks to significantly increase processing capacity.
So he is contemplating asking GPs to act as gatekeepers to the testing system, which would mean those wanting a test could only get one if their local doctor were to authorise it.
But introducing GP screening would undermine the timeliness of the data, since it would add at least another 24 hours to the process of wanting or needing a test and getting the result.
I understand Hancock is very reluctant to assign this responsibility to GPs but he may have no alternative.