Testing capacity has become a focal point in public debate, and for good reason. Experts in epidemiology believe that, in the absence of a vaccine for Covid-19, testing provides governments with one of the best means of monitoring their epidemics and getting them under control.

In Britain, when the government released its Five Pillar Plan on testing on 2 April, it aimed to reach the ability to conduct 25,000 tests per day among those in hospitals and the vital frontline healthcare workers in the NHS “by mid to late April”.

The Health Secretary Matt Hancock astonished his colleagues and went further when he said he wants to increase total testing capacity to 100,000 per day by the end of the month. Care workers have also been added to government’s list of priorities this week.

So how is the UK doing so far? Well, the 40 NHS labs and eight Public Health England labs which have now been mobilised are theoretically able to process about 25,000 PCR tests per day, as of Thursday, 16 April, according to the Health Secretary. Private labs which have been drafted into the government’s efforts are now providing further capacity on top of this.

But according to the Department of Health and Social Care and Public Health England, 21,328 tests tests were carried out in the 24 hours between 9am on Thursday 16 April and 9am on Friday 17 April. The capacity may be there, but we are not quite reaching the optimum number of possible tests, even if the trend is steadily climbing upwards.

By international standards, too, the UK does seem to be lagging behind in numerical terms. According to the crude estimates of Our World in Data, Britain had conducted more tests for the virus per thousand people in its population than France, Portugal, New Zealand, and the United States on 10 March.

Yet according to their calculations for 16 April, the UK now lags behind all of these countries, some of them by quite a significant margin. Our low testing numbers appear to be a significant outlier.

So what explains the difficulties the UK is currently experiencing in increasing testing numbers?

One significant element is probably government policy. The UK shifted its testing strategy on 12 March as it entered the “Delay” phase of its pandemic, agreeing to concentrate its testing resources on those who were showing symptoms of Covid-19 in hospitals rather than widespread testing in the community. The government decided to opt for targeted rather than mass testing, a decision possibly influenced by the need to use scarce resources carefully.

Initially, also, Britain suffered from being a late starter in the global race to test, test, and test even more.

Britain only began rolling out its PCR testing programme on 10 February, by which time the reagents, complex biological molecules required to produce results in the PCR tests, were in short supply.

On top of this, the UK was slow in getting the private sector involved. Where private biotech and diagnostics companies led the efforts to produce large numbers of tests in Germany and South Korea from January, the British government and Public Health England only began getting private companies involved in the national effort towards the end of March.

But now that the UK has launched its private sector and public health lab networks, the sluggish upward trend in testing is confusing. From private labs are emerging tales of baffled researchers, who had been expecting to be deluged with swabs, finding themselves with too little to do.

This makes little sense, when the government received a significant boost on 9 April after the US diagnostics firm Thermo Fisher said it would help to supply reagents, testing kits, and chemicals to help the UK hit its 100,000 mark. Of course, it is not yet clear how far this has alleviated all supply-side shortages.

So why is the UK only gradually climbing towards higher test numbers?

Some of the ongoing pressures may be due to the process of PCR testing. It is not a quick procedure. It requires accurate samples to be taken carefully. These samples are then sent to laboratories, where they are tested by trained staff using specialist machinery. When transportation is factored in, it currently takes about 24 hours in the UK between testing and getting a result back. Time-saving technologies are on the way, but will take time to become widely available.

Still, the challenges of the process are not entirely unique to the UK, even if they are compounded by the way in which our biotech sector is orientated towards knowledge production rather than large-scale manufacturing. This cannot explain all of the UK’s ongoing difficulties.

Again, it may be a conscious decisions made by the public health authorities not to test more people yet.

On 16 April, the deputy chief executive of NHS providers, Saffron Cordery, said that she believes the UK’s testing is on track, and that the authorities will soon be able to begin testing the community much more widely.

“We need to be careful about letting the 100,000 target drive perverse behaviour”, Cordery said. She then added that “we shouldn’t be forcing anyone – staff or patients – to have a test if it’s not needed, just so the target can be met.”

“A number of trust leaders tell us that they have now tested or are able to test all the staff and patients they feel they need to, on the current testing approach.”

Cordery now believes the country is ready for a change of approach: “As we know, until a vaccine is ready, comprehensive testing is the route out of social distancing and lockdown.”

But gravely important questions remain unanswered by the authorities. If several NHS trusts are succeeding in testing those who most need it, is it not time to expand community testing? If not, why not?

It is not yet clear whether Britain is suffering from a logistical challenge in mobilising its full testing capacity, or if this is a conscious policy choice. Are the authorities failing on testing or are they saving our testing capacity for when it will make the most impact? The government still has much to clarify.

Sorting this out as soon as possible – and providing more clarity on what the policy actually is – will be crucial if the UK is going to be able to develop a way of moving out of the current lockdown. To shut down future outbreaks, to allow workers to go quickly for tests if they feel unwell, to isolate care homes by establishing that no residents have the virus, all depends on a robust system that can test large numbers day in, day out.

Reaching the targets for testing capacity will be necessary before the government can begin managing the cautious, and long, return to normality. Indeed, the problems on testing may help explain why Britain looks likely to end up with full lockdown for longer than other comparable countries.