The prime minister said he took “full responsibility” for the underperformance, which Labour blames for the government “losing control” of Covid-19 amid a spike in infections which has prompted new restrictions.
Johnson has in recent weeks repeatedly attempted to defend NHS Test and Trace and its boss, the Tory peer Baroness Dido Harding, from “unseemly” attacks.
But the service again saw a fall in its contact-tracing rate last week, which was for the 14th week running below (at 71.6%) the 80% figure the government’s scientific advisers have said is needed to make the entire policy viable.
HuffPost UK has also heard stories of people being told to travel hundreds of miles for tests, including a Somerset mum who was told to go to Northern Ireland.
The PM, who recently attempted to claim testing and tracing had “very little or nothing to do with the spread and transmission” of coronavirus, told BBC London: “Of course there are people who’ve had bad experiences and I apologise for the bad experiences that people have had with NHS Test and Trace but it is a fact that we are conducting more tests than any other European countries, 20 million people have been tested.
“Yes, it is true that in London, it’s not been as fast as elsewhere but we are seeing a rise in cases now, alas.
“Because we came together as a country, we got the numbers down and I’m afraid some of the muscle memory has faded.”
He added: “I, of course, take full responsibility for everything the government has done.”
The PM meanwhile suggested he might ease the rule of six to allow families to be together at Christmas.
Asked by ITV Anglia whether he was telling families of five they could not have both grandparents over for Christmas lunch, Johnson said: “We are not saying that at all, we’ll do everything we can... to make sure that Christmas for everybody is as normal as possible.”
Meanwhile, Johnson told his father, Stanley Johnson, he should wear a face covering in confined spaces, after the 80 year-old was pictured shopping without a mask.
Asked by BBC Points West what advice he would give Johnson senior, the PM said: “Well the same advice as I would give anybody in my family, anybody in this country – follow the guidance – hands, space, face, wear a mask if you’re in a confined space and get a test if you have symptoms; rule of six people do understand.
“I do think that it will work and we will start to see progress but it does rely on people doing it together.”
This article originally appeared on HuffPost UK and has been updated.