The reproduction or R rate for the Coronavirus is of limited value, at least as a single national figure.  It doesn’t tell one who has the disease and where – in other words, what local rates are.

So if for example there is a rise concentrated in hospitals and care homes, as some claim there is at present, this will drive any upward increase in R, which would therefore be misleading as an indicator of that rate elsewhere.

In any event, that national figure will have a range, and will be out of date when announced, because the testing, death and admissions data takes time to come in.

Furthermore, R is subject to distortion.  Consider the virus in care homes and hospitals.  It is driving up R because heir own R average was higher to start with, and they now represent a greater share of the overall R average.

All this may help to explain why, if one reads between the lines, the Government is subtly loosening the ties that bind it to R.

In his recent address to the nation, Boris Johnson showed a slide with five bands, each of which represents a different alert level.  The lower the level, the less the restriction.

Ministers’ aim at present is to get the UK down from level four (at which transmission is “high or rising exponentially” to level three (at which the Coronavirus is simply “in general circulation”).

The Prime Minister said that these levels will be determined “primarily by R” [our italic].  That leaves quite a lot of wiggle room for the new Joint Biosecurity Centre, which will be responsible for setting the alert levels.

(Clearly, the Government’s three stages of reopening are linked to these five levels.  Were the JBC to declare on May 31 that the UK is now at level five, for example, school reopenings would presumably be off.)

Jenny Harries, the Deputy Chief Medical Officer, gave an indication how this room for manoeuvre might be used at last Friday’s daily Government press conference.

She said that “the real outcome is the reduction in the number of cases, that is our focus, not the R”.  And it isn’t hard to see how the gradual rollout of test and trace could give the JBC further flexibility.

For the more people are tested – Johnson’s recent announcement of a testing capacity of 200,000 by the end of this month has not been officially discared – the more will be known about local R-rates.

That would potentially give the Government the opportunity to run a more locally varied lockdown.  ConservativeHome pushed the idea last week, and Fraser Nelson has suggested lifting the shutdown in London.

This site has to report that we are finding little enthusiasm among Ministers for anything other than a national approach.

Those we spoke to yesterday were very sceptical, on the ground that controlling the movement of people between different areas would be very difficult – and that localities themselves display considerable variations in R.

And as we wrote yesterday senior NHS figures and epidemiologist advisers are wary of “complicating the message” – a concern that will be shared in parts of Downing Street.

If the Government sticks to national rules with no local variation, the effect will be to stretch the lockdown – with the runners necessary moving, as it were, at the pace of the slowest of the pack.