Government coronavirus measures based on infection doubling rate of four days - not five it said, writes Robert Peston

There was widespread anxiety and concern that the government was basing its measures to suppress spread of coronavirus on an assumption that the numbers infected were doubling every five days, when the evidence here and internationally suggested doubling rate of nearer four days.

I raised this concern with Neil Ferguson, the Imperial College expert whose forecasting has underpinned the government's accelerated moves to constrain our freedom of movement.

He told me: "I misspoke when I said five days".

His baseline for the spread rate (R0) is that each sufferer would infect 2.4 people on average (technically: R0 = 2.4) which implies that the numbers infected would double every 4.3 days, in line with the international data.

If R0 turns out to be 2.6, then the doubling rate would be less than 4 days, and an R0 of 2.0 would mean doubling every 4.6 days.

The hope is that the doubling rate is nearer to five days than three, but the important point is that the government's preventative action plan is conditioned by expectation of doubling around every four days.

Which believe it or not is reassuring, because it suggests that if we do what the government is asking us to do in limiting our social interaction (and it is by no means clear we will) then the risk of the NHS collapsing under the weight of Covid-19 has been significantly reduced.