The government has defended NHS Test and Trace after it emerged the system will have a radical overhaul.
People who have been in contact with confirmed coronavirus cases could get home visits if tracers are unable to reach them over the phone and 6,000 national contact tracing jobs will be cut in a fortnight.
The number of tracers will drop from 18,000 to 12,000 as the system becomes more localised.
Labour said the scheme was nowhere near “world-beating” but the government insists NHS Test and Trace is a “successful system”.
Earlier this month, scientists warned that Test and Trace needed a dramatic improvement if a second wave of coronavirus was to be avoided after schools reopen in September.
On Tuesday, junior health minister Edward Argar said Test and Trace, run by labour hire company Serco, would now operate as a “hybrid system”.
He told BBC Radio 4’s Today programme: “We’re reducing the number of contact tracers nationally through that Serco contract from 18,000 to 12,000, and throughout we have worked closely with local public health officials, but we are strengthening further that relationship, so you will still have that national calling, that national push to make contact.
“But for those hard to reach or for those people who can’t be contacted, then you’ve got this door-to-door approach as well.”
Argar told Sky News: “This is a reflection of a successful system that, as we've always said, will flex and evolve to meet our understanding of the disease and the changing needs of our communities.
"We are making contact with just shy of 80% of those who test positive and then we are making contact with around a similar amount of their contacts.
"We've traced a quarter of a million in the space of about two and half months, that is a significant achievement.
“This is a reflection of an effective system built up rapidly that is now evolving to reflect the changing needs of local lockdowns and a local-centric approach."
But Labour said the contract with Serco was "ineffective and not fit for purpose", and that the service should be led by directors of public health and supported by primary care and NHS labs.
Shadow health minister Justin Madders said: "Labour has been calling for a locally-led contact tracing system for months - it's welcome that local authorities are now finally being given additional support to tackle the virus in their areas.
"But it's clear Boris Johnson's £10bn centralised contact tracing system is nowhere near 'world-beating' as he claims and the system is unable to fight local outbreaks successfully."
The latest official figures show that in the seven days to 29 July, 72.4% of people identified as being in contact with an infected person were reached and asked to self-isolate by NHS Test and Trace, a drop from 76.2% the previous week.
The prime minister told MPs on 20 May the test-and-trace operation would be "world-beating" and in place by the start of June.
Argar, who previously worked for Serco, said he ”had no involvement with this process and with this contract".
He told BBC Radio 4's Today programme: "I spent some time working with Serco before I was an MP, I left there six years ago.
"I was head of public affairs. That was not a management or director position at all.”
Professor Paul Hunter, professor of medicine at the University of East Anglia, said a tracing system "will only work well if it's done close to the population".
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