Boris Johnson’s Test and Trace service has hit another new low after it reported its worst ever figures for tracking down “close contacts” of people with Covid.

The prime minister has recently admitted that the service run by Dido Harding has to get better and hopes the second nationwide lockdown that began on Thursday will give it time to improve.

But the latest statistics showed that the controversial £12bn system saw just 59.9% of cases in England being reached and told to self-isolate to stop the spread of the virus. The figure is down from 60.6% for the previous week.

That means that for the week ending October 28, 40.1% of people who have been in contact with someone testing positive for the virus have not been reached – and therefore not told to self-isolate for 14 days.

A total of 131,136 known people were not reached in that week, meaning they were potentially spreading the virus asymptomatically.

Since the service began, some 598,930 close contacts have not been reached, compared to 1.2m who have.

The figure is the worst since the so-called NHS Test and Trace service, which is largely run by private companies, was launched in May.

The previous worst figure for close contacts was 60% in the week to October 14.

Government scientific experts have advised that the whole system can only work effectively if at least 80% of “close contacts” are actually tracked down and self-isolate

Close contacts are defined as those who have spent more than 15 minutes within two metres of a positive Covid case.

Earlier, justice secretary Robert Buckland said the month-long lockdown that began on Thursday would be used to “redouble our efforts” to expand the NHS Test and Trace programme.

The statistics once again show a big difference in success rates between council-run local teams and the partly outsourced NHS Test and Trace call centres.

For cases managed by local health protection teams, a much higher 97.9% of contacts were reached and asked to self-isolate in the week to October 28.

For cases managed either online or by call centres, 58.5% of close contacts were reached and asked to self-isolate.

There is no record of whether any of those people actually did self-isolate.

Shadow health minister Justin Madders said: “Seeing again that over 40% of people not being contacted is a continued failure of test and trace.

“Ministers know that we won’t get on top of the virus unless we see a better performing system. Despite the flurry of government announcements on testing this week we haven’t heard a single proposal on how they are going to fix contact tracing.

“It is absolutely vital they use this time in the second lockdown to finally fix test and trace.”

Harding defended the service, pointing to it hitting the PM’s target for 500,000 daily testing capacity by the end of October.

“Latest figures show NHS Test and Trace is processing more tests and reaching more people, which means we are finding positive cases and helping to break chains of transmission,” she said.

“We know that there are areas where we still need to improve and we are working tirelessly to make the service quicker and more effective every day.”

The figures for testing turnaround times also showed the service was still a long way from the PM’s target of getting 100% of tests done within 24 hours.

Just 26.4% of people tested for Covid-19 in England at a regional site, local site or mobile testing unit – a so-called “in-person” test – received their result within 24 hours.

The proportion was up slightly from 22.6% in the previous week, but Johnson told MPs earlier this summer that he would get “all tests turned around by the end of June”.

A total of 137,180 people tested positive for coronavirus at least once in England between October 22 and October 28.

Of those transferred to the contact tracing system, 82.7% were reached and asked to provide information about their contacts.

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