"Mass public testing has never been our strategy for any pandemic that I’m aware of," he told The Telegraph.

"The current problem is based upon the fact that we didn't invest in preparedness before all this happened.

"We always knew that when it came to a pandemic, it was a case of when, not if. But there has been a focus on influenza preparedness. And for things like influenza, mass testing is not important, and it never figured as a potential strategy. Public Health England are central to the whole thing.

"The focus was on pandemic influenza and that's because it happens on a much more regular basis. Pandemics with other viruses happen more rarely - but they do happen, because HIV is a virus, Sars was a potential pandemic, Mers was another one, and Ebola. It was always understood that the next big pandemic could be a virus, but actually it was probably more likely to be influenza than any other, because we know that happens on a regular basis.

"It was always known that this was going to happen at some point, and the preparedness requires that you have planned for it, and they have been planning for it but there hasn't been the investment, and that’s why we're in this situation.

"In hindsight, I would have brought in 200 more laboratory roles in October. You can call it a mistake, but on the other hand, you can say it was just pragmatic and the Government didn't want to invest millions of pounds into something that is about preparedness, rather than a real situation in front of them at the time.

"Testing can be extremely powerful, and we now desperately need it at a population level to be able to understand what’s going on. The best data we have is hospitalisations and deaths, so we're always lagging behind a little bit, whereas getting the serology would give us a much better idea of what's actually going on.

"At the end of it we'll be able to look back and say that was probably the wrong thing to do, and perhaps we didn’t make the right decision."

In 2008, a potential flu pandemic was listed at the top of the National Risk Register of threats to the UK.

Prof Medley said that emergency planners decided mass testing would not be effective during a flu outbreak because the disease had different characteristics to more dangerous threats like coronavirus.

"Mass testing isn't appropriate for influenza because it has a much smaller duration of infection. And the symptoms don’t start until you're infectious," he said.

Prof Medley conceded, however, that UK officials had been aware of South Korea's mass public testing strategy, launched after the Sars outbreak ended in 2004.

"The South Koreans developed mass testing because they had an experience with Sars and so they obviously decided that was a potential way forward for them," he said.

Even so, the UK Government's preparations appeared to conflict with official guidance on bird flu issued to countries by the World Health Organization (WHO).

In an advisory document released in 2005, titled Responding To The Avian Influenza Pandemic Threat, the WHO advised countries to ready themselves for mass testing in the event of a major influenza outbreak.

"Because the initial symptoms of H5N1 (bird flu) infection mimic those of many diseases common in these countries, accurate case detection requires the testing of large numbers of samples,” the document warned.

"Improved local capacity is therefore a more rational solution."

There are now major questions over Britain's preparations for a pandemic. Last week, The Telegraph revealed that the NHS failed a major cross-government test of its ability to handle an outbreak four years ago, but the "terrifying" results were kept secret from the public.

Codenamed Exercise Cygnus, the three-day dry run for an influenza pandemic carried out in October 2016 found that Britain would be quickly overwhelmed by a severe outbreak due to a shortage of critical care beds, morgue capacity and personal protective equipment (PPE).

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