Chris Hopson, chief executive of NHS Providers said: "Early results from a very small sample suggest that there is a significant potential prize here in terms of the number of staff who could return to work.
"But it is striking how many trusts are also reporting significant constraints due to swab and reagent shortages. Trust leaders will do the very best they can with the resources they have available. But these shortages, which trusts do not control, need to be overcome if we are to see the growth in testing capacity we are all looking for."
Scientists have explained some of the reasons why the UK has struggled to source enough testing kits.
Stephen Baker, professor of molecular microbiology at the University of Cambridge, said: "There is a massive demand for raw materials and commercial kits, this is not unique to the UK, and many places no longer have stock of essential reagents."
Robin May, professor of infectious diseases at the University of Birmingham, said increasing production of raw materials for testing kits, and ensuring quality control for the large numbers of kits needed, were two problems being faced. "Tackling all of these rate-limiting steps together to eliminate all of the bottlenecks is the primary reason why testing has been relatively slow to roll-out so far," he said.
During Wednesday's daily Downing Street coronavirus briefing, Dr Yvonne Doyle, the current medical director at PHE, said the "intention" for testing NHS frontline staff was "to get from thousands to hundreds of thousands within the coming weeks".
However, on the evening the Prime Minister spoke of the importance of testing for getting on top of COVID-19, Prof Jonathan Van-Tam, England's deputy chief medical officer, described testing as a "side issue", telling ITV'sPestonprogramme that the focus should remain on social distancing.
During today's Downing Street briefing, Matt Hanock is reportedly expected to outline how testing capacity could be increased by paying private firms to carry out swab testing, roll out antibody tests, and conduct randomised sampling of the population.
There have been recent reports that offers of help from some UK scientific institutions to boost testing rates have been ignored by medical officials.
The Francis Crick Institute announced today it hadrepurposed its laboratoriesso that by early next week, scientists should have the capacity to be conducting around 500 tests a day, or 3000 each week. In the longer term, it said it hoped to achieve 2000 a day.
It said results could be returned within 24 hours, enabling NHS staff to return to work as quickly as possible.
Sir Paul Nurse, the Institute's director, said: "Institutes like ours are coming together with a Dunkirk spirit – small boats that collectively can have a huge impact on the national endeavour."
Meanwhile, the University of Cambridge said it was behind anew rapid diagnostic test for COVID-19. It said the SAMBA II machines, developed by Diagnostics for the Real World, could diagnose the infection in less than 90 minutes.
The University said the tests were being deployed in Cambridge hospitals ahead of a nationwide launch.
