Coronavirus tests for NHS frontline staff are to be trialled this weekend ahead of a wider roll-out to help those given the all-clear from the disease to return to work.
Cabinet minister Michael Gove said the Government was working in a "new alliance" with universities, businesses and researchers to boost testing capacity.
It comes as Prime Minister Boris Johnson faces leading the country's response to the Covid-19 outbreak from isolation after he tested positive for the virus.
Two of his key lieutenants will also remain in self-isolation this weekend, after Health Secretary Matt Hancock confirmed he had coronavirus and England's chief medical officer Professor Chris Whitty exhibited symptoms.
Commenting on the testing plans on Friday, Mr Gove said: "This will be antigen testing - testing whether people currently have the disease - so that our health and social care workers can have security in the knowledge that they are safe to return to work if their test is negative.
"These tests will be trialled for people on the front line starting immediately, with hundreds to take place by the end of the weekend - dramatically scaling up next week."
NHS chief executive Sir Simon Stevens said the tests would initially be focused on those working in intensive care, A&E, GP practices and staff running ambulance services.
The testing announcement comes as:
- The editor of British medical journal The Lancet, Richard Horton, wrote that NHS bosses had not heeded pandemic warnings that could have prevented "chaos and panic" in the "wholly unprepared" health system.
- Relatives of Britons on the Zaandam cruise ship off the coast of Panama expressed fears after four passengers died on board and more than 130 people reported flu-like symptoms.
- The Government asked local authorities in England to house all rough sleepers and those in hostels and night shelters by the weekend.
- Sir Simon announced the go-ahead had been given for two new temporary hospitals being built in Birmingham and Manchester.
MPs on the Health and Social Care Committee in the House of Commons were warned earlier this week that NHS staff rotas were under strain.
Workers have been forced to stay at home as a result of following Government guidance to self-isolate when showing Covid-19 symptoms, such as a temperature or cough.
The expanded testing will be free, with those getting a negative result able to return to work, the Department of Health and Social Care said.
The Government plans to open a laboratory to analyse samples this weekend, with the aim of carrying out about 800 tests at designated sites in hotspot areas such as London and then scaled up in the weeks to come.
The testing comes as a total of 759 people died in UK hospitals after being diagnosed with coronavirus, while 113,777 tested positive and hundreds of thousands more are thought to be infected.
It is likely Prof Whitty will be awaiting results of his own test for the virus, while there will be concerns in Government over who could be affected next.
Chancellor Rishi Sunak and Cabinet Secretary Sir Mark Sedwill have both been with the Prime Minister in recent days, but had displayed no symptoms on Friday night and therefore had not been tested.
Mr Gove said the diagnosis of Mr Johnson and Mr Hancock showed the "virus does not discriminate", warning: "We are all at risk."