Video report by ITV News Health and Social Affairs Correspondent Emily Morgan
Downing Street has confirmed "just 2,000 frontline NHS England staff have been tested for coronavirus," despite 1.2 million people working for the health service.
It comes as the government is coming under increasing pressure to ramp up coronavirus tests as healthcare leaders warned there is "no immediate prospect" of mass NHS staff testing.
Housing and Communities Secretary Robert Jenrick admitted on Wednesday only 900 NHS staff had been tested over the weekend as the programme is rolled out.
He told Radio 4’s Today programme: "Clearly that’s a low number but one we want to build on significantly."
Chris Hopson, the chief executive of NHS Providers, which represents NHS trusts, said maximum testing capacity in the UK was currently “very constrained” at around 13,000 tests per day.
Mr Jenrick reiterated the need to expand testing, telling ITV News that the Government would be able to ramp up capacity to 25,000 a day by mid-April.
The minister said: "Testing is essential to our strategy and that is why we are investing so much in it. The number of tests in increasing, it is rising."
"This week it will reach 15,000, then 25,000 by mid-April," he added.
Mr Jenrick denied the Government and Public Health England (PHE) would only agree to centralised testing after claims from scientists and universities that their offers of help have been rejected.
At present, the focus is on testing patients in hospital to see if they have coronavirus, with NHS trusts told earlier in the week they should use up to 15% of any spare testing capacity for NHS staff.
He said the Government was willing to "work with any provider" who had the "right infrastructure and skills" and urged them to get in touch.
Asked when the national coronavirus testing centre near Milton Keynes would be fully operational, Mr Jenrick replied: "I don’t know precisely when that’s going to be coming on board."
The chief executive at NHS Providers has said one NHS trust can only test three staff members a day due to a lack of swabs.
Chris Hopson told BBC Radio 4’s The World At One programme: "Our sense is once that decision is made and that 15% threshold is lifted then our trusts will be able to start testing a lot more staff, but, the key thing to understand is it’s the swabs and the reagent shortages that is the problem.
"So I was talking to a trust this morning that can only test three members of staff a day because that’s the number of swabs they’ve got."
He added: "I was talking to the largest trust, one of the largest trusts in the country this morning who basically want to test many, many hundreds of their staff but they actually can’t because they’ve got a reagent shortage."
PM admits testing is way to 'unlock the coronavirus puzzle'
Prime Minister Boris Johnson, who is self-isolating after testing positive for Covid-19, said testing was “how we would unlock the coronavirus puzzle” and “defeat it in the end”.
In a video message on Twitter on Wednesday night, he said: “What we need to do is massively ramp up not just tests, so you can know whether you’ve had the disease in the past – the so-called antibody test – because that will enable you to go to work in the confidence you cannot be infected or infectious.
“Second, people need to know they haven’t got it rather than isolating themselves at home for no reason – that’s very very important above all for our NHS staff.
“It’s crucial people who do have the disease are able to be tested positive and to take the necessary steps to isolate at home in the way that I am doing and many many others are doing.”
He added: “I just want to reassure that although I am sequestered here in No.10 Downing Street I am, thanks to the miracles of modern technology able to be in constant touch with my officials and everybody in various departments across the whole of Whitehall.”
On Tuesday, Cabinet minister Michael Gove acknowledged at the daily Number 10 news conference that the Government needed to go "further, faster" on testing.
But he warned that a shortage of the chemical reagents needed for the tests was proving to be a “critical constraint” on the Government’s ability to ramp up capacity.
NHS staff have expressed frustration that they are being forced to self-isolate just as they are most needed, because tests are not available to show whether they are clear of the disease.
Mr Hopson said of the weekend data: "Only around 15% of those in 14 day isolation tested positive so other 85% could come back to work. If anything like right, a huge opportunity.
"However, before getting carried away, remember testing capacity is still v constrained (currently 13k/day) and there are 1.2 million NHS staff. So no immediate prospect of mass staff testing."
Public Health England (PHE) has also come under fire over wider testing of members of the public with Covid-19.
PHE has said repeatedly most adults in good health who develop symptoms will fully recover and do not need to be tested.
However, many scientists disagree and have said it is only through widespread testing that the UK will be able to emerge from lockdown.
On Tuesday, former World Health Organisation director Prof Anthony Costello said the UK has the capacity to test hundreds of thousands more people.
He said: "By mass testing, we can detect new outbreaks and there will be much less disruption rather than isolating the whole economy.
"We have 44 molecular virology labs in the UK. If they were doing 400 tests a day, we would be up to Germany levels of testing (around 70,000 a day) and that is perfectly feasible."
Coronavirus: Everything you need to know