Robert Peston: Was the government right to restrict coronavirus testing?
When the government announced that anyone with a cough or a temperature had to stay home for a week, that was framed by the chief medical officer and the chief scientific adviser as a policy designed to slow the peak of the coming coronavirus epidemic.
And it should help to do that.
But there was another decision taken that many doctors tell me was more important, and was in their view retrograde - which was that anyone with mild symptoms who does not require hospitalisation would not be tested for it.
Those with symptoms are not even being asked to voluntarily click on a button on a website or send in a text to announce that they may have the virus.
This means the government has little precise data on where the virus is, and whether there are burgeoning hot-spots that should be ring-fenced and cut off from the rest of the country, to delay its spread.
In other words there is in an inbuilt fatalism in the government's policy, which is that - in the apparent view of the scientists and politicians - there is no way to prevent the virus coursing through the population and that the most policy can hope to achieve is to lower the peaks of infection.
The former World Health Organisation director Anthony Costello has been eloquent in expressing the views of many, that this is highly risky.
His argument is that the only countries in the world that have significantly reduced the rate of increase of infection - China, Singapore, Taiwan, Korea, Hong Kong - have done so by mass testing of potential sufferers and coerced isolation of those infected.
He repeatedly cites the WHO's owns orthodoxy in praise of this approach.
So the question that I have repeatedly put to ministers and officials is why we have rejected this strategy. And I have not had a compelling answer.
It is true that there is currently a laboratory capacity to do only 4000 tests per day, according to Public Health England, and an ambition to provide at least 10,000 a day.
Given that officials believe there are probably more than 10,000 British people with the virus now (significantly more than the official count of 1372) the labs would be swamped if everyone who thinks they have symptoms was tested - and there is also a question about whether there are enough trained and available medical staff to carry out the swabs and process the tests.
But if there is a wartime mobilisation effort to massively expand the production of oxygen ventilators, which there is, why isn't there a similar expedited effort to dramatically expand testing?
Why is the government being an activist in trying to buy life-saving equipment to keep alive the acutely ill but being less of an activist in throwing money at resources that could significantly reduce the rate of infection?
The only answer we appear to have is that officials and ministers fear that if a Chinese-style plan to curb the outbreak actually worked, it would be disaster postponed rather than prevented.
The fundamental fear of the PM and his advisers appears to be that if the outbreak is only modest in the coming few weeks, it would rear its lethal head again next winter when the NHS would be less able to cope.
This is a message I've had repeatedly communicated to me.
Hence all the focus on the UK population acquiring so-called "herd immunity" as I mentioned on Thursday, for all the Health Hecretary Matt Hancock's rowing back on this yesterday.
But with a virus like this, surely time is the most precious resource we have.
And if we can buy a few months grace from the most extreme of outbreaks, would it be beyond the government's capability to use those months to very significantly expand the NHS's capacity and reorganise care so that it better meets these extreme needs?
Though just possibly it is already too late.
Even so, I remain puzzled by the government's approach, not least because given how many British people probably already have the virus, and given the current rate of spread (which is probably a doubling in the number of cases every four days, on the basis of European data) we are set to run out of ventilators in a very short number of weeks.
Which is why this week feels to me like perhaps the most important for the PM, and his main advisers, Chris Whitty and Sir Patrick Vallance, in their effort to minimise the impact of Covid19.
What they decide - for example at today's Cobra meeting - may have irreversible consequences, for better or ill.