More than three weeks ago NHS England announced it would scale up testing capacity to 10,000 a day, but the number of people tested has struggled to pass 8,000 a day.
More than 10,000 people were tested in a single day for the first time on April 1.
At that rate it would take more than 18 years for each person in the UK to be tested.
Health bosses on Wednesday night claimed that the country has the necessary laboratories to carry out 100,000 tests a day – eight times the current stated capacity – but does not have the swabs and reagents needed to detect the virus.
Other countries are understood to have ordered the raw materials before the UK.
Germany, which is considered to be one of the best-prepared countries in tackling the crisis, is carrying out an estimated 500,000 tests per week and has a death toll of 1,444, roughly a third of the UK's total.
It comes after the World Health Organisation (WHO) insisted that members who are battling the virus have to scale up their response to the crisis.
'Ramping up' testing
WHO director-general Tedros Adhanom Ghebreyesus has previously criticised countries which have not tested enough, telling them: "you cannot fight a fire blindfolded... test, test, test".
The government's response comes as chief scientific advisor Sir Patrick Vallance said there needed to be "a big increase in testing".
Despite the capacity for 4,000 tests a day, less than half that number were being used until the number of confirmed cases in the UK passed 500 – on March 12.
According to data from Public Health England, on March 31 10,412 tests were carried out, but only 7,511 people were tested.
The number is lower due to double counting - to "double check a negative result" or "an inconclusive first test". Some people need different samples taken, using more than one test kit.
Who can get tested?
As the UK moved from the 'contain' to 'delay' phase of its response to the virus, the criteria for testing narrowed to only the most severe cases.
Public Health England said it needed to "prioritise testing for those most at risk of severe illness from the virus", and recommended that people in the community exhibiting symptoms "do not usually need testing".
Testing was previously limited only to those who had returned from an affected country or had been in contact with a known case.
Instead, tests will primarily be given to:
- all patients in critical care for pneumonia, acute respiratory distress syndrome (ARDS) or flu-like illness
- all other patients requiring admission to hospital for pneumonia, ARDS or flu-like illness
- where an outbreak has occurred in a residential or care setting, for example long-term care facility or prison
See how the tests work below
How does the UK compare to other countries?
In the early stages of the epidemic, ministers and public health officials decided to follow a different strategy from much of the rest of the world: to mitigate rather than suppress the spread of the virus.
Widespread testing would not be required, it was decided, given the majority of the population was predicted to contract the virus anyway. Instead, priority was given to relieving pressure on the NHS by buying up much-needed ventilators and making space for intensive care beds.
On March 12, all community contact tracing was abandoned as it became clear the virus was spreading freely, and the number of people who have now been tested for the disease passed 150,000 on March 31.
Based on the latest data from April 1, per head, it is one of the lowest rates in Europe, behind Denmark, Germany, Italy and Austria.
The UK tested just over 2,300 people per million of the population (152,979), while Austria tested more than 6,300 per million (55,863), and Italy tested almost 9,000 per million (541,423).
Since shifting focus to patients in hospitals, the case detection rate in the UK as been improving, and now sits at just below 20%, in line with Austria.
With the exception of Italy, one of the worst-hit countries in Europe, most countries with mass testing have lower detection rates and are picking up more cases.
Buy testing more of its population and tracing their contacts early, Germany, Norway and South Korea have kept the number of new cases low.
Germany has now tested more than 10,000 people of every million in its population, but has just 749 cases per million, a 7.5% detection rate.
South Korea, often cited as the prime example of a good testing regime, has tested more than 8,000 people per million and has picked up 191 cases per million.
Italy has now tested almost 9,000 people per million in the country (541,423 tests), with a detection rate of 20%.
Accuracy of testing is equally important.
Norway has tested 1.77% of the total population, but only 4.9% of those were confirmed to have the disease.
Since shifting focus to patients in hospitals, the case detection rate in the UK as been growing, and now sits at just below 20%, in line with Austria.
Why is it important?
By focusing testing on suspected cases in hospital as the UK has, it becomes far more difficult to assess the true scale of infection in the country and treat cases earlier.
Countries who cast the net further are able to pick up more cases and follow the spread more closely, acting earlier to avoid being overwhelmed.
After the first case was discovered in Germany the country began aggressive contact tracing and mass testing was engaged early on. Similarly in South Korea, contact tracing and wide-scale testing have been key.
“Germany has had a very aggressive testing process,” Dr Mike Ryan, health emergencies director at the World Health Organisation (WHO) said. “So the number of tests maybe detecting more mild cases.
“From the beginning, we have very systematically called upon our doctors to test people,” Prof Lothar Wieler of Germany’s Robert Koch Institute said.
It has led to exceptionally low death rates in countries with larger testing regimes.
Currently Germany has seen 1,444 deaths despite detecting 96,000 cases - a mortality rate of 1.5%.
South Korea, which has now tested more than 420,000 people, has 177 deaths from more than 10,000 recorded cases - a mortality rate of 1.8%.
But those countries which began testing late, including in the UK, have focused on the more severe cases - those most likely to die.
Consequently mortality rates in the UK are much higher, at 8.6 per cent.
Concentrating effort on the sickest has other knock-on effects.
On Wednesday, Chris Hopson, chief executive of NHS Providers, which represents hospital trusts, said latest figures suggest that as many 180,000 NHS staff were “self-isolating” but that around 85 per cent of these – 150,000 workers – could be cleared to return to work.
Former health secretaries and medical experts have said the Government’s handling of the issue was “ridiculous”.
Jeremy Hunt said: “It is clear that the only way to avoid an Italian-style meltdown is to follow what has happened in Korea and Germany and that means mass testing in the community.”
Stephen Dorrell, the health secretary from 1995 to 1997, said: “It is ridiculous that there are NHS staff sitting at home feeling perfectly healthy and we can’t allow them to get back to work.”