The nation’s test and trace system could be being hampered due to public reluctance to answer calls from an unknown number, a government adviser has said.
Data released last week shows two in five close contacts of people who tested positive for coronavirus in England are still not being reached by NHS callers.
Only 60.3 per cent of close contacts of positive cases were reached by NHS Test and Trace in the week ending 21 October due to people not picking up their phones.
Conversely, nearly all contacts were reached in the same week in cases managed by local health protection teams.
For cases handled either online or by call centres, the figure was 58.1 per cent.
Dr Susan Hopkins, a public health expert and adviser to NHS Test and Trace, told BBC Breakfast: "Firstly, the teams make every effort to call individuals. We do need to get people's contact details from the primary case.
"Usually, about one in five individuals, there's no contact details given. So we struggle to find that individual and then cases through the system.
"People don't answer their phones, people don't want to get a contact from an unknown number.
"And that's part of the reason why there's increasing local contact tracing, working with directors of public health and local councils, so that their local system can find some of these individuals that the national system cannot."
A number of experts have urged ministers to use the forthcoming lockdown to ensure that the test and trace system is up to scratch.
On Saturday, Dr David Strain, senior clinical lecturer at the University of Exeter, said: "In order to minimise the impact of the lockdown on the mental and physical health of the nation as well as the economy, this needs to be accompanied by a clear exit strategy, including an overhauling of the Test and Trace system to ensure it is fit for purpose."
On the lockdown, Dr Hopkins, who is also deputy director of Public Health England's National Infection Service, said there was a "fine balancing act" about when to implement a lockdown.
She told Times Radio’s Breakfast: "I think that even if we had done a lockdown earlier, it's likely we would probably need one again later on. So there's a fine balancing act about when this occurs.
"What the lockdown is there to do is to reduce the number of cases and ideally half them, or even reduce them further than that.
"So what we need to be able to do is see that now, and see that we're able to effectively do that, and that means the whole of society to be ready to take the steps with us to reduce our transmissions and reduce our contacts."
Additional reporting by PA
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