Ministers shrugged off warnings a lack of tests could cost lives, until they were forced to change tack

On 11 March, the day before Boris Johnson told the nation that the coronavirus sweeping the UK could no longer be contained and that testing for Covid-19 would stop except for the seriously ill in hospital, the head of No 10’s “nudge unit” gave a brief interview to the BBC.

At the time it was barely noticed – it was budget day, after all. With hindsight, it seems astonishing.

“There’s going to be a point, assuming the epidemic flows and grows as it will do, where you want to cocoon, to protect those at-risk groups so they don’t catch the disease,” said Dr David Halpern. “By the time they come out of their cocooning, herd immunity has been achieved in the rest of the population.”

Play Video 5:58 Coronavirus tests: how they work and what they show

It was a window into the thinking of the political strategists directing the UK response to Covid-19, who claimed to base what they were doing on scientific evidence. We would let the disease spread among the healthy. So no need to test.

If there was a moment when the UK turned its back on the traditional public health approach to fighting an epidemic, this was it.

Quick guide What to do if you have coronavirus symptoms in the UK Show Hide Symptoms are defined by the NHS as either: a high temperature - you feel hot to touch on your chest or back

a new continuous cough - this means you've started coughing repeatedly NHS advice is that anyone with symptoms should stay at home for at least 7 days.

If you live with other people, they should stay at home for at least 14 days, to avoid spreading the infection outside the home. After 14 days, anyone you live with who does not have symptoms can return to their normal routine. But, if anyone in your home gets symptoms, they should stay at home for 7 days from the day their symptoms start. Even if it means they're at home for longer than 14 days. If you live with someone who is 70 or over, has a long-term condition, is pregnant or has a weakened immune system, try to find somewhere else for them to stay for 14 days. If you have to stay at home together, try to keep away from each other as much as possible. After 7 days, if you no longer have a high temperature you can return to your normal routine. If you still have a high temperature, stay at home until your temperature returns to normal. If you still have a cough after 7 days, but your temperature is normal, you do not need to continue staying at home. A cough can last for several weeks after the infection has gone.

Staying at home means you should: not go to work, school or public areas

not use public transport or taxis

not have visitors, such as friends and family, in your home

not go out to buy food or collect medicine – order them by phone or online, or ask someone else to drop them off at your home You can use your garden, if you have one. You can also leave the house to exercise – but stay at least 2 metres away from other people. If you have symptoms of coronavirus, use the NHS 111 coronavirus service to find out what to do. Source: NHS England on 23 March 2020

Ebola, Sars, Mers – in previous epidemics, nobody had questioned the need to hunt down and eliminate the virus by testing everyone with symptoms, tracking their contacts and isolating and testing those people in turn. But not this time.

“You can’t fight a fire blindfold,” said Dr Tedros Adhanom Ghebreyesus, the director general of the World Health Organization, just five days after the UK switched course in what sounded like an urgent appeal to Johnson, Halpern and any fellow travellers.

“You can’t stop this pandemic if you don’t know who is infected. We have a simple message for all countries: test, test, test. Test every suspected case. If they test positive, isolate them and find out who they have been in close contact with up to two days before they developed symptoms and test those people too.”

But his warnings were shrugged off by government ministers in the UK – public health experts had been sidelined and a newer breed of scientist was in favour at No 10.

According to Richard Horton, editor-in-chief of the Lancet medical journal, the dominant voices in the Scientific Advisory Group for Emergencies (Sage), the scientific expert group advising the government, were mathematical modellers and behavioural scientists, including Halpern.

On 25 March, Horton told MPs on the science and technology select committee that Sage appeared to have little input from public health experts and doctors, despite being chaired by the chief medical officer, Chris Whitty, and the chief scientific officer, Sir Patrick Vallance.

The clue for Horton was in the main papers it considered in advising the government of the strategy.

“There is evidence on modelling and on behavioural science, but I don’t see the evidence from the public health community or from the clinical community,” he explained.

Testing, isolation and quarantine – basic public health interventions – were barely on the agenda. Warnings from Chinese scientists of the severity of Covid-19 had not been understood.

“We thought we could have a controlled epidemic. We thought we could manage that epidemic over the course of March and April, push the curve to the right, build up herd immunity and that way we could protect people,” said Horton. “The reason why that strategy was wrong is it didn’t recognise that 20% of people infected would end up with severe critical illness. The evidence was there at the end of January.”

Anthony Costello, a UK paediatrician and former director of the WHO, also fiercely criticised the decision to stop tests. “For me and the WHO people I have spoken to, this is absolutely the wrong policy,” he said. “The basic public health approach is playing second fiddle to mathematical modelling.”

Less than two weeks on from the lockdown that Johnson announced on 23 March, the original strategy, the decisions that came before and after it, and the UK’s inability to ramp up testing for NHS staff – let alone anyone else – are under unrelenting scrutiny.

Ministers have been flailing. What has emerged is a picture of confusion and uncertainty at the top, with ministers making promises they cannot keep and apparently with little comprehension of the global tussle for tests that may make it impossible for the UK to buy its way belatedly out of the problem.

The UK is now competing with every other nation to obtain the kits it needs, particularly the polymerase chain reaction (PCR) test, which tells someone whether they have Covid-19 or not.

The Guardian has been told that presidents and prime ministers are trying to outbid each other to secure these kits and their components, which are in short supply. The US also has woken up to the need to test – and is telling companies that export them that America must come first.

No wonder, perhaps, the UK now finds itself struggling to increase testing to 25,000 a day for hospital patients and health workers, let alone meet its ambition – once stated but now seldom mentioned – to reach 100,000 a day, to include other key workers.

“In all countries we have prime ministers calling the CEOs and diagnostic companies to try to get hold of the stocks. Indonesia and Peru we know have offered to order several million tests and send private planes to pick the tests up. There is more going on behind the scenes to secure supplies,” said Dr Catharina Boehme, chief executive of the non-profit Geneva-based Foundation for Innovative New Diagnostics, which is a WHO collaborating centre.

The companies are trying to be responsible, she said. “They supply small quantities to each country to give sufficient supplies for a number of days and then ship on a very frequent basis. But there is clearly this move in the US where several companies have openly declared they can’t supply anyone outside the US.”

Three US companies making the PCR tests, Abbott, Hologic and Cepheid, have been told not to export them, leaving Africa – which uses their technology in HIV tests – with a single supplier, Roche in Switzerland.

The WHO, Unicef and the Bill & Melinda Gates Foundation are working on procuring tests for low- and middle-income countries. There are global shortages even of the swabs, which are made by companies in just two countries, the US and Italy.

In the UK, the testing regime has also been hampered by the lack of laboratory capacity to analyse the samples – a warehouse in Milton Keynes has been set up with the laboratory facilities to add capacity.

In the long term, hopes are pinned on blood tests for antibodies produced by the immune system fighting the infection, which will show who has had Covid-19 and is probably therefore immune. These could be a game-changer, allowing key workers out of isolation, for instance to reopen schools.

But another sign of the disconnect between public health experts and Downing Street became evident last Wednesday. Prof Sharon Peacock, director of infections at Public Health England, told MPs that millions of home testing kits would be available, delivered by Amazon or bought in Boots, within days, not weeks.

“Tests are being ordered across Europe and elsewhere and purchased in south-east Asia. This is widespread practice. We are not alone in doing this,” she said.

But within hours, Whitty seemed to quash the idea. He warned that antibody tests needed proper evaluation, which was being undertaken at Oxford University. “The key thing for us to do is evaluate. Are these tests accurate enough to be used by the general public?” he said at the prime minister’s press conference the same day.

The health secretary, Matt Hancock, has said the government had bought 3.5m antibody tests, but the Guardian understands the UK has actually put in orders for 40m more. It is the sort of drastic gamble that governments around the world are taking, afraid that stocks will disappear.

Antibody tests are available right now on the internet to anyone who wants them – but some are unreliable, and could give the wrong verdict. So far, the best are 90% sensitive to Covid-19 and 90% specific.

The perils are all too apparent, and not just for the antibody tests: Spain and the Czech Republic recently had to send back hundreds of thousands of antigen tests to China because they had an accurate detection rate of just 30%.

Antibody tests are being used widely in China and South Korea, where the virus has already been beaten down to lower levels by the traditional PCR testing of those with symptoms and tracing and isolating their contacts.

Mass contact tracing, which can be highly labour-intensive, is made possible through phone apps, which alert people who have been near someone who has tested positive.

The concept was greeted with horror by some in the UK as mass data gathering and an invasion of privacy – yet Oxford University is now developing just such an app.

Looking ahead to the endgame, testing and tracing contacts, figuring out where the virus has been and who is still vulnerable is widely acknowledged among scientists to be the way to stamp out the last pockets of a pandemic.

For now, Italy is doing more testing than any other country, desperate to bring down its cases and fatality rates.

Not far behind is Germany, which has been doing widespread testing of suspects with symptoms and contact tracing in the WHO-recommended fashion from the beginning. Its efforts are being led by the renowned public health body, the Robert Koch Institute.

Facebook Twitter Pinterest A research assistant holds coronavirus test samples at the Lower Saxony state office for consumer protection and food safety in Hanover, Germany. Photograph: Peter Steffen/AP

And while they are the first to say the pandemic is in its early stages and could yet explode in Germany, the rise in cases and deaths has not been not as sharp as in the UK and nowhere near the levels seen in Italy and Spain.

It remains to be seen whether the new UK attention to testing can help bring the numbers down here as well. In a few short weeks, a strategy that rejected old science for new seems to have unravelled – and testing has suddenly become central to the fight against Covid-19.

Testing is being carried out in hospitals, new and old, and in places such as the huge vacant car park of Chessington World of Adventures in Surrey, where every ride stands still.

Under temporary canvas roofs, nurses in wind-blown plastic aprons, gloves and masks lean into open car windows to swab the nose and back of the mouth of healthcare workers, who may have the telltale dry cough, or are isolating because their child or partner has.