There is little chance of safe escape from lockdown restrictions unless NHS Test and Trace is picking up most of those infected with coronavirus, and those who have come into contact with them.
How is it doing so far?
It is early days, but it looks as though only around one in nine of those with the illness are being reached.
Here are the numbers that imply too few infected people are being contacted.
According to government data, details of around 1,160 per day were passed to the tracers, of whom only 770 were actually contacted.
That compares with between 1,500 and 2,000 people per day who tested positive.
It is not at all clear why so few of those testing positive were reached.
But such is not the most disturbing data.
More worrying is that there are around 4,500 new infections per day in the community according to the Office of National Statistics (ONS).
But the ONS survey takes no account of infections in hospitals and healthcare settings.
It is reasonable to assume that around a third of all infections are in hospitals.
So that suggests daily infections are more than 6,500.
In other words just 770 of 6,500 people are having the kind of conversations with tracers that would allow those tracers to get in touch with those who have been in close proximity with infected people - a ratio of roughly one in nine.
Which is far too few to deliver confidence that the system will either put sufficient numbers of potentially infected people into quarantine to suppress the spread of the dreadful virus or will yield the kind of granular local data that can facilitate localised lockdowns as and when there are flare ups rather than economically devastating regional or national lockdowns.
Right now we have a test and trace system that is expensive but a long way from doing the job it has been set.
If there is another serious flare up before it is fit for purpose, we are in trouble.
PS. One obvious way of improving coverage of infected people would be to routinely test everyone working in hospitals or staying in hospitals every fortnight or so.
Coronavirus: Everything you need to know