Covid: In ignoring his scientists, Boris Johnson has taken his biggest risk, writes Robert Peston

Boris Johnson's decided against implementing a circuit breaker national lockdown. Credit: PA

It is important to understand the gap between the prime minister and the scientists and experts on the Scientific Advisory Group for Emergencies (Sage), because it is huge.

The point is that Sage on September 21, when evidence was accumulating that infections were on the rise, recommended a series of national measures. These included closures of pubs and restaurants and hairdressers everywhere, for example, or more severe restrictions on our freedoms in short sharp national "circuit breakers".

By contrast, Boris Johnson has adopted a regional approach to stamping out coronavirus. And even the "baseline" measures he is imposing on areas such as Merseyside considered to be "very high" risk are seen as inadequate by his scientific advisers - as his chief medical officer Chris Whitty told me at the press conference yesterday.

What I can't judge is whether the prime minister has made a brave judgement that the economic costs of following his scientists' advice will do more net harm - including to health - than following what they recommend.

Or whether he has made a more cynical judgement that too many of his supporters are fed up with restrictions on their freedoms, and that he lacks the political capital - or the backbone - to tell them they are wrong.

Boris Johnson announced the three-tier system on Monday. Credit: PA

The stakes for him could not be higher. Sage is saying that without more decisive interventions, the first onerous lockdown will have been almost for nothing - because there will be a second massive hump of hospitalisations and deaths in the coming three months.

This delay rather than elimination of catastrophe was precisely what Whitty and his colleagues feared would happen, when they agonised about imposing the initial lockdown.

So if the second hump becomes a reality, and having been warned, it is not obvious that the prime minister's authority would ever recover.

PS His authority has not exactly been reinforced by Sage's reflection that the billions of pounds he has deployed on creating NHS Test and Trace is having only "a marginal effect on [Covid-19] transmission".