How CAN we fight the virus if we don’t know who’s got it?

As Boris faces urgent calls to ramp up tests to lock down infection hotspots...

numbers of tests, and the Government is also said to be looking at whether university and private sites could be used to expand capacity. It is still unclear who will get access to the additional tests when they are finally offered.

Mr Johnson has said healthcare workers will be a priority so that they can continue to work and not self-isolate unnecessarily. But there are still no official plans which detail how this will be done. Meanwhile, doctors have taken to social media to complain about the risks they face, while some hospitals are said to be acting unilaterally, ordering their own tests to prevent staff shortages.

Dr Pankhania says key workers – such as those involved in providing essential services including food deliveries, electricity and gas – should also be tested. Proof of how vital testing is can been seen by looking overseas. South Korea has carried out more tests than any other country – 4,000 per million residents, four times as many as Italy. Up to 20,000 are carried out a day and anyone who wants a test can visit one of 50 drive-through testing stations.

South Korea has recorded almost 8,800 cases – more than double the UK total – but far fewer deaths.

Like the UK, Italy has performed only limited tests – and the nation has surpassed China in terms of deaths. But in the region of Veneto, there was a mass testing campaign. Italian biologist and disease expert Andrea Crisanti, who ran the campaign, says: ‘The moment we find a sufferer, we test all their friends, relatives and neighbourhood.’

This has proved crucial because – as is emerging from the evidence

– many people who are infected may show only mild symptoms, or even no symptoms at all.

In one town, Vo’ Euganeo, Prof Crisanti tested all 3,300 residents and, of 89 who were positive and quarantined, half had no symptoms. Within days, the town had no new cases. Prof Cristanti says: ‘It’s the invisible positives with no symptoms who are most worrying.

‘For the UK I would advise systematic testing and targeted lockdowns where clusters are found.’

It means there is increasing pressure on the Government to roll out a DIY test to help experts to map the virus’s spread more accurately. Known as antibody or serological tests, they have been used in China, South Korea and Italy.

Mr Johnson announced last week that the Government was in negotiations to buy a ‘game-changing’ test that was as simple as a pregnancy test. ‘If it works as its proponents claim, we will buy hundreds of thousands,’ he said.

These finger-prick tests involve taking a blood sample and identifying antibodies which the body develops in response to the infection. They can provide a much quicker result – possibly within minutes – and at a similar cost.

But while it has been broadly welcomed, there is scepticism about its accuracy and how helpful the tests could be. Sir Patrick admitted it could be ‘weeks or months’ until they are ready, and cautioned that it might not be ‘reliable enough’.

Another antibody test is being developed by Public Health England (PHE) in order to track the virus in the community. It could tell who has had the virus previously, and could help the Government work out how far the outbreak could still spread. PHE said it would begin using the test ‘shortly’ with 1,500 tests a week in the first instance. Dr Pankhania says: ‘The antibody test has its uses but not in an active outbreak when what we need to do is control infection rates. Some may not have produced enough antibodies to prove they’ve been infected. It isn’t precise e nough.’

THE other way to be tested is privately – if you can afford it. London’s Private Harley Street Clinic is offering a £375 test which can be delivered to your home – and director Dr Mark Ali says he has sold thousands. Clients include celebrities and executives.

The tests involve taking swabs from the nostrils and throat and sending them to a UK laboratory, which returns the results within three working days.

Dr Pankhania says the test, which looks for genetic material produced by the virus, appeared to be similar to the NHS test. But the clinic failed to respond to questions about it.

A team from the engineering science department at Oxford University is developing a more rapid test which could deliver a result in 30 minutes. But these, and the latest Government promise to increase testing, may all come too late, warns Dr Pankhania. ‘We need testing now – we need to know where the threats are coming from. Think about a tsunami coming. What can you do about it after the wave has gone and everything has been destroyed?’