Boris Johnson has confessed to “frustrations” at the test and trace system and admitted there is need to “improve” the programme.
Latest figures show that less than 60% of close contacts of people who tested positive for coronavirus in England are being reached.
Meanwhile, just 15% of people tested for COVID-19 in England at an in-person site are receiving their result within 24 hours.
Challenged about the performance of the test and trace system at a Downing Street news conference, the prime minister said: “I share people’s frustrations and I understand totally why we do need to see faster turnaround times and we need to improve it.
“We need to make sure that people who do get a positive test self-isolate – that’s absolutely crucial if this thing is going to work in the way that it can.”
Mr Johnson previously promised a “world-beating” national test and trace scheme.
Sir Patrick Vallance, the government’s chief scientific adviser, also admitted there was “room for improvement” in the test and trace scheme.
“The testing system has ramped up the numbers they’re able to do quite effectively, but it’s really important to concentrate on numbers of contacts, isolation as quickly as you can, and getting things back as quickly as you can ideally to get the whole process done within 48 hours,” he said.
“It’s very clear there’s room for improvement on all of that and therefore that would be diminishing the effectiveness of this.”
However, Sir Patrick cautioned that the “effectiveness” of test and trace was less when there are higher numbers of coronavirus infections.