or over two months now, Britain’s public health specialists have been asking why the government abandoned the basic infection-control practice of “test, trace, isolate”. Most of us have suggested that a system to do this was a precondition of easing the lockdown. The key words in Boris Johnson’s speech on Sunday were “you should go to work if you can’t work from home”. He made no mention of preparations for tracing and testing contacts of people who test positive for Covid-19. In the plan published today, a newly appointed test and trace taskforce will begin to develop such a system. The countries that have succeeded in taming their coronavirus epidemics – such as South Korea, Taiwan, China, Australia and New Zealand – differ from the UK in many ways. But they all have in common “test, trace, isolate” as the centrepiece of their strategy. The UK government claims to be “following the science”, but it seems the science now needs to catch up with a government that is prioritising concerns about economic damage over epidemic control. The economic damage is clear, and the lockdown will also have knock-on health effects due to unemployment, domestic abuse, and postponed diagnoses and treatments. But if science is the rationale, why not level with the public and show the data that suggests the return to work is now the lesser evil? If there is evidence from modelling that social distancing while at work or commuting – rather than sheltering at home – is sufficient for virus control, let us see it. The government may have reasons to lift the lockdown before a “test, trace, isolate” system is in place but we do not know what they are. Some will see an ongoing commitment to “herd immunity” behind the lack of public health actions in the speech. However, I believe no UK government would select this as the preferred scenario. And emerging antibody data from hard-hit cities such as New York show that, with less than a quarter of the population affected, it would take at least another wave of devastation to get close to the herd immunity threshold. It is possible that the data shows that there is still too much virus circulating in Britain and that a tracing system would be overwhelmed. Johnson hinted at this when he said that the quarantining of arriving travellers would be imposed only “with transmission significantly lower” – in other words, imported virus is still just a fraction of domestic virus transmission. If that is the case, however, telling people to go back to work is very risky advice. It is also probable that the testing system does not yet have the required capacity, or that not enough contact tracers have been hired. However, there is unused capacity in local councils that the government is choosing not to tap. The mantra for the past seven weeks has been to “protect the NHS” by staying at home. Surely the intent was also to use this time to prepare for the calibrated end to the lockdown. What we got in the prime minister’s speech was advice to go back to work this week without using public transport (unless we can work from home), and a promise to reimpose the lockdown if Covid-19 flared up again. What we did not get was any list of the actions in place to pursue and contain the virus. All this is reminiscent of another government soundbite, “the right steps at the right time”. That idea did not work out so well at the start of the epidemic – when mixed messages and a stuttering set of interventions resulted in the virus spreading. On Sunday Johnson said: “We have been through the initial peak.” He is quite right that coming down the mountain is “often more dangerous” – particularly if the peak was higher than it needed to be – but why make the descent even more perilous by refusing to deploy all the tools to hand. No mountaineer would do so without the right equipment. What many public health specialists hoped to hear was a commitment not only to scaling up testing but to deploying it in a more targeted manner. A commitment to work in partnership with the devolved governments and the regional and local authorities. And a commitment to use the tests to reduce virus transmission. If the government has decided these actions are premature then, at the very least, the piloting of these strategies needs to take place. Those defending the government’s Covid-19 response have reasonably pointed out that policy mistakes are always clearer in retrospect. So let me make a prediction. If we take the prime minister’s advice and return to work in large numbers now – and without the ability to test, trace and isolate – then virus spread will increase, there will be super-spreader events and local or regional lockdowns will have to be reconsidered. The prime minister implied in his speech that relapse will somehow be our fault – we were not sufficiently “alert”. The responsibility will lie, however, with a government that has encouraged a premature return to work before the epidemiologic conditions and interventions were in place to make it safe to do so. David Hunter is the Richard Doll professor of epidemiology and medicine in the Nuffield Department of Population Health, University of Oxford