The government is under pressure to explain how it will meet its target of increasing coronavirus testing ten-fold by the end of April.
Health Secretary Matt Hancock has said he wants 100,000 tests to be carried out every day.
But Labour said there were no details on how this could be achieved and what sort of testing would be involved.
It comes as a field hospital with capacity for up to 4,000 patients is to be opened in east London.
London’s new NHS Nightingale Hospital will treat intensive care Covid-19 patients in the temporary facility at the ExCel convention centre.
Speaking on Thursday at the Downing Street coronavirus briefing, following days of criticism of the government’s record on testing, Mr Hancock announced a “five-pillar” plan to reach the