The government now has the capacity to test around 12,750 people a day for coronavirus - but official figures show that only around 8,000 tests are carried out each day.
The prime minister repeatedly promised that testing would be ramped up throughout March and gave a target of 10,000 tests a day.
But despite testing capacity reaching nearly 13,000, the highest number of tests in one day has only reached 9,793.
In the past week, an average of just over 8,000 tests have been carried out each day:
A total of 152,979 Covid-19 tests have been carried out in the UK to date.
The government is facing increasing pressure to ensure that frontline NHS staff are prioritised for testing as hospitals across the UK face staff shortages due to staff members having to self-isolate without knowing if they have the virus.
Housing and communities secretary Robert Jenrick told the BBC's Today programme that growing capacity would mean a higher number of frontline NHS staff could be tested.
Testing for NHS staff was rolled out at the weekend and the government has now said that over 2,000 NHS staff members have been tested.
Mr Jenrick said: “We now have capacity today to be testing 12,750 people and we expect that within a couple of days to be 15,000.
"So we should now have the growing capacity to test NHS staff in addition to the patients in critical care."
He added that the target of testing 25,000 people a day should be met by "the middle of April".
However, NHS medical director Professor Stephen Powis told LBC that the next few weeks would see "hundreds of thousands of tests a day".
“We are getting the kit… you heard me correctly, we need to get to hundreds of thousands of tests a day, and we will do that over the course of the next few weeks,” he told the radio station.
Labour’s shadow health secretary Jonathan Ashworth has called on the government to explain why there have not been more tests to date.
He questioned why the UK was lagging behind in testing numbers compared to Germany, where he said half a million people a week are being tested.
Cabinet minister Michael Gove had previously said that a shortage of the chemical reagents needed for the tests was proving to be a “critical constraint” on the UK's ability to ramp up capacity.
Public Health England has said repeatedly that most adults in good health who develop symptoms will fully recover and do not need to be tested.
However, many scientists disagree and say it is only through widespread testing that the UK will be able to emerge from lockdown.
The World Health Organisation has consistently urged countries to test every suspected case of coronavirus.