What should the British government be trying to achieve with this week’s switch to a “lockdown” strategy?

It is embarking on a policy that will not just affect everybody in the country, but will impose huge costs, for months. The government must be able to explain this strategy if it is to carry the public with it. It also has to do a far better job of explaining how the country might return to something closer to normal than it has managed to achieve hitherto.

Model The British government has been dragged into adopting a lockdown model adopted by the great majority of western high-income countries – Sweden is the principal exception, although the US may soon join it.

The aim now is to suppress the virus. A previous strategy of developing “herd immunity”, while mitigating the consequences for the health system by spreading infections out over time, has been abandoned. Rightly so, since allowing the 60 per cent of the population to be infected that is necessary for herd immunity, could, based on ratios in an influential study from Imperial College London, mean 530,000 patients in intensive care and 360,000 deaths.

UK intensive care capacity would be exhausted many times over if this were to occur. Actual deaths would then also be substantially higher than the estimates above.

That policy has been abandoned. So what now? Prime Minister Boris Johnson said, in announcing the lockdown, that “we will keep these restrictions under constant review. We will look again in three weeks, and relax them if the evidence shows we are able to”. But what evidence will he use? How might restrictions be lifted? He did not say.

Measures We must also recognise that both the virus and the measures taken to tackle it impose huge economic costs. Nouriel Roubini of New York University calls what is coming a “Greater Depression”, quite possibly worse than that of the 1930s.

Harvard’s Carmen Reinhart writes that “this time truly is different”. Desperate times require desperate measures. Roman Frydman, also of NYU, and Nobel laureate Edmund Phelps argue that these measures must include redirecting resources to ensure production of goods and services needed to tackle the health emergency.

US president Donald Trump is foremost among those who argue that the cure must not be worse than the disease. This is not absurd. We should indeed take the least socially costly option.

Lives are valuable, but they are not infinitely so. That is particularly true of the lives of older people (like me). Even with the best possible policies of amelioration, a depression would itself impose not only economic costs, but harm mental and physical health, too.

Yet this does not mean the best policy would be to lift controls as soon as possible. On the contrary, as US senator Lindsey Graham, normally a pro-Trump stalwart, has noted, “there is no functioning economy unless we control the virus”. People have stopped meeting, spending and going out to work because they are frightened.

Lifting lockdowns will not diminish these fears. On the contrary, it would increase worries about the healthcare system’s ability to treat anything important. The fear would be over whether the system itself will evaporate.

Yet, the economic and social costs of the lockdowns do seem likely to increase exponentially over time. A few months could be bearable. More will not be. The lockdown must be used to expand, train and deploy an enlarged healthcare workforce and ramp up testing capacity massively.

It must become possible to quarantine all contacts of infected people. A crucial role will also be played by tests that identify people who are immune and able to go back to work.

Policy In brief, the best health policy seems also to be the best economic policy. This is to suppress the disease by bringing the full resources of the state to bear upon it, thereby allowing the fastest possible return to near-normality. Since this policy precludes herd immunity, the disease will remain a threat until a vaccine is available.

This being so, comprehensive testing has to play a central role. Success with suppression in some countries will also create new challenges – notably including travel between countries, some of which are letting the virus rip through their populations, while others seek to suppress it.

After blundering about with one strategy and then being forced to adopt something less intolerable, the UK government has to make it quite clear that the lockdown will not be over in three weeks.

It needs to explain clearly and precisely what its objectives are, how it will use this period to allow a return to something closer to normality after it ends, what it is doing to strengthen the country’s ability to manage the disease in the medium and longer term, and what we might be returning to.

Uncertainty Needless to say, that will also depend on what other countries do. The illusion of sovereignty cannot survive this crisis.

There are no certainties in a situation of such uncertainty. But it looks as if, far too late, the government has adopted the least bad policy, while also doing a decent job of insuring people against the huge economic costs of the crisis. But the closure of the economy cannot last very long.