Prime minister Boris Johnson has been accused of presiding over "intergalactic incompetence" after nearly 16,000 positive COVID-19 test results were left off the UK's daily tally.
Sir Keir Starmer, leader of the UK's main opposition party, Labour, made the claim in parliament on Wednesday.
Some 15,841 cases were left off the UK daily test figures between September 25 and October 2, due to an error with some of the Microsoft Excel data files - being used to log the figures - exceeding the maximum size.
The error prompted fears potentially infectious people had been missed by contact tracers and not told to self-isolate.
Starmer asked if Johnson could accept that the error had "put lives at risk".
He added: "12 billion pounds has been invested in this system. And yet a basic Excel error brings it down. No wonder it's been described as intergalactic incompetence. So why at this crucial moment did it take so long to catch this error and to address it?"
Striking back, Johnson assured the "computer glitch" had since been fixed, and said his opposition "can't have it both ways" by blaming both Excel and humans.
He added that the 16,000 cases "don't change the basic distribution of the disease".
The fiery midweek confrontation follows days of criticism after the government revealed an artificial daily high of 22,961 cases to be added to the UK's COVID-19 count on Monday.
This number accounted for the delay in publishing 15,841 extra cases that accidentally went unreported in England between September 25 and October 2.
Following the revelation, Public Health England assured that all those who received positive test results had been advised to self-isolate and that it was simply a glitch in the database system.
Back in parliament, Starmer also challenged his political rival about localised restrictions in place across parts of the UK, particularly in the north.
He pointed especially to towns that have been under extra measures for a number of weeks but have still seen their cases skyrocket.
This includes Burnley, which was at 21 cases per 100,000 people when restrictions were imposed but has since jumped to 434.
Bolton, meanwhile, was at 18 cases per 100,000 people and is now at 255.
"If the prime minister can't see or hear local communities when they say the infection rate has gone up tenfold under restrictions, and he doesn't realise that's a problem, then that is part of the problem," Mr Starmer argued.
He then quipped: "If you actually listen to the question, we might get along better."
But Johnson was firm in his response as he insisted he had already explained why COVID-19 "continues to spread".
He said: "I wish I could pretend that everything was going to be rosy in the Midlands or indeed in London.
"Alas, we are also seeing infections rise, and that's why we need a concerted national effort.
"We need to follow the guidance."