In mid-February a colleague mentioned that for the first time in his life he was more concerned than his mother, who had been relatively blase about the risks of Covid-19. It felt odd for him to be telling her to take care. We are both professors in a department of infectious disease epidemiology, and we were worried.

Two months on, that anxiety has not gone, although it’s also been joined by a sense of sadness. It’s now clear that so many people have died, and so many more are desperately ill, simply because our politicians refused to listen to and act on advice. Scientists like us said lock down earlier; we said test, trace, isolate. But they decided they knew better.

Am I being unfair? The government assures us that its decisions and timing are based on science, as if it is a neutral, value-free process resulting in a specific set of instructions. In reality, the science around coronavirus is in its infancy and developing daily, with researchers across the world trying to understand how the virus spreads, how the body responds – and how to treat it and control it. The speed at which our knowledge has increased is impressive, from the sequencing of the virus in January through to having candidate vaccines in early February.

Mathematical models are being refined to predict the extent and speed of spread and estimate the impact of control methods. My own group is studying the response of communities, showing how the epidemic is amplifying existing social inequalities. People with the lowest household income are far less likely, but no less willing, to be able to work from home or to self-isolate.

But while scientists carry out observations and experiments, testing, iterating and discovering new knowledge, it is the role of policymakers to act on the best available evidence. In the context of a rapidly growing threat, that means listening to experts with experience of responding to previous epidemics.

When I say that politicians “refused to listen”, I am referring to the advice and recommendations coming from the World Health Organization, from China and from Italy. The WHO advice, based on decades of experience and widely accepted by public health leaders and scientists around the world was clear – use every possible tool to suppress transmission. That meant testing and isolating cases, tracing and quarantining contacts, and ramping up hygiene efforts.

The UK did well in the early phase, but then, on 12 March, the government alarmed many public health experts by abruptly abandoning containment and announcing that community case-finding and contact-tracing would stop. The aim was no longer to stop people getting it, but to slow it down while protecting the vulnerable.

The evidence underpinning the government’s decision appears in a report from 9 March summarising the potential impact of behavioural and social interventions. The report did not consider the impact of case-finding and contact-tracing, but it did suggest that the biggest impact on cases and deaths would come from social distancing and the protection of vulnerable groups.

And yet social distancing was not recommended then. That day, 12 March, after hearing with disbelief the government announcement that didn’t include widespread social distancing, I recommended to my team at Imperial that they should work from home for the foreseeable future. Indeed, I have not been to my office since.

Neither the advice nor the science were followed that week. My colleagues, led by Neil Ferguson, published a report on 16 March estimating that without strong suppression, 250,000 people could die in the UK. The government responded that day with a recommendation for social distancing, avoiding pubs and working from home if possible. But there was still no enforcement, and it was left up to individuals and employers to decide what to do. Many people were willing but unable to comply as we showed in a report on 20 March. It was only on 23 March that a more stringent lockdown and economic support was announced.

Between 12 and 23 March, tens, if not hundreds of thousands, of people will have been infected. Boris Johnson himself may well have been infected that week, and his stay in the intensive care unit may have been avoided if the government had shifted to remote working on 12 March. The current best estimate is that around 1% of those infected will die.

So where to now? Once again, public health experience, including modelling, leads to some very clear recommendations. First, find cases in the community as well as hospitals and care homes; isolate them, and trace their contacts using a combination of local public health teams and digital tools.

Second, know your epidemic. Track the epidemic nationally and locally using NHS, public health and digital surveillance to see where cases are continuing to spread. This will be essential so that we can start to lift the lockdown while shielding the population from hotspots of transmission. Build community resilience by providing local support for vulnerable people affected by the virus and the negative impact of the control measures.

Third, ensure transmission is suppressed in hospitals, care homes and workplaces through the right protective equipment, testing, distancing and hygiene. Investigate the differential effects on black and minority ethnic groups, and provide appropriate protection.

Fourth, ensure that the most vulnerable, socially and medically, are fully protected through simple access to a basic income, rights for migrants, and safety for those affected by domestic violence.

Many, including the Labour leader, Keir Starmer, say that now is not the time for blame. I am not looking to blame – but for scrutiny so that lessons can be learned to guide our response. We need to avoid further mistakes, and ensure that the government is hearing, and acting on, the best advice.