Fewer than half of coronavirus tests are being used, No10 has revealed.
In the 24 hours to 9am Tuesday, only 18,206 out of possible 41,398 tests were carried out.
That means only 44% of available capacity was used.
In the 24 hours to 9am Tuesday, just 18,206 out of possible 41,398 tests were carried out.
That means only 44% of available capacity was used.
The first of four mobile test units was expected to operational by tomorrow.
No10 confirmed its goal remained to carry out 100,000 tests a day by next Thursday (April 30).
The PM's spokesman said: “We are making progress in increasing the capacity but we do need to ensure that we are making full use of it.”
First Secretary Dominic Raab, standing in for Boris Johnson at Prime Minister's Questions, admitted the Government needed an “exponential increase” in testing to hit its target.
Mr Raab told MPs: “In the final week that will require a big increase.
"But, of course, with a project like this, it does require an exponential increase in the final days and the final week of the programme."
Keir Starmer tore into the Government's testing plan for NHS workers, saying it was flawed with an "obvious problem".
In his first Commons outing as Labour leader, Mr Starmer said: "If a care worker has symptoms of coronavirus or a family member has symptoms, he or she has to self-isolate, quite rightly.
“To get a necessary test, they are then instructed to travel to a testing centre, which is often very many miles away.”
He added: “There's an obvious problem with that system – not all care workers will have access to a car, because they've got symptoms or family members have got symptoms they obviously can't use public transport, so it is little wonder we're seeing these pictures of half-empty testing centres.”
Shadow Health Minister Dr Rosena Allin-Khan, an accident and emergency doctor, tweeted: "The Government needs to ensure the number of tests carried out reaches 100,000 per day by the end of April.
“Capacity is irrelevant if it's not used.
"We can't get a grip on the coronavirus crisis without understanding how widespread the pandemic is."
In a statement to the Commons, Health Secretary Matt Hancock said demand for tests was "lower than expected".
He said: "I've set the goal of 100,000 tests a day by the end of this month and I'm delighted to say that the expansion of capacity is ahead of plans, even though demand has, thus far, been lower than expected.
"We are therefore ramping up the availability of this testing and expanding who is eligible for testing, and making it easier to access the tests."
Health workers' leaders called for volunteers to be mobilised so tests could increase.
Unison union general secretary Dave Prentis said: “Clearly ministers' strategy isn’t working, despite checks being vital in winning the fight against Covid.
“We need to get tests to staff, not expect them to attend test centres.
“There has to be a better way of taking testing to staff on the frontline.
“It’s not sensible to expect poorly individuals to travel miles from home to be swabbed.
“That could mean several hours’ drive for some living in remote areas, which is totally unrealistic.
“People also need to be tested within days of the onset of symptoms.
“It’s no surprise take up has been so low. The Government must make it easier for staff if there’s to be any possibility of meeting its100,000 a day goal.
“We want to work with the government to identify how to use the help of the army of volunteers who’ve signed up to assist the NHS.
“Many have yet to be given anything to do. They could be mobilised to take kits to NHS and care workers.”
The boss of one of the world’s biggest pharmaceutical companies said the UK was struggling to ramp up testing because the Government had failed to spend enough cash on healthcare “over many years”.
Roche chief executive Severin Schwan told BBC Newsnight: “You can't fix the infrastructure in a couple of weeks.
“If there is too little investment over many years into the health care system, then it's simply not possible to ramp up as fast as you would wish in such a challenging situation.
“The real issue here is that the UK has probably not invested enough into healthcare, both in absolute terms and in relative terms over many years.
“That was a problem to start with, but it really shows up in such a crisis when the system is more stressed.”
