The weekly rate of new Covid-19 cases has increased in dozens of areas of England after an Excel spreadsheet error meant almost 16,000 cases went unreported.
The systems failure has also created a delay by the country's NHS Test and Trace to find the contacts of those who tested positive for the virus, in some cases by around a week.
It comes as Britain remains the worst-hit European country, yesterday passing its latest milestone of 500,000 confirmed coronavirus infections.
Meanwhile, British Prime Minister Boris Johnson was unable to say this morning how many contacts of positive cases had been missed.
According to analysis of Public Health England (PHE) data published on Sunday night, Manchester now has the highest rate in England, with 2,740 cases recorded in the seven days to 1 October - the equivalent of 495.6 cases per 100,000 people, up from 223.2 in the previous week.
Liverpool has the second highest rate, up from 287.1 to 456.4, with 2,273 new cases. Knowsley in Merseyside is in third place, up from 300.3 to 452.1, with 682 new cases.
There have also been sharp rises in Newcastle upon Tyne, Nottingham, Leeds and Sheffield.
Scientists are now concerned that potentially thousands of people who are contacts of those with Covid-19 may have spread the virus in the last week.
The issue occurred when people who tested positive were not recorded once a master Excel spreadsheet reached its maximum size, which stopped new names being added in an automated process.
The files have now been split into smaller multiple files to prevent the issue happening again.
PHE said the technical issue resulted in 15,841 cases between September 25 and October 2 being left out of the reported daily coronavirus cases.
It said the outstanding cases were transferred to NHS Test and Trace "immediately" after the issue was noted and all cases were passed on to tracers by 1am on Saturday.
Dr Duncan Robertson, lecturer in management sciences and analytics at Loughborough University and fellow of St Catherine's College, Oxford, said the error was "an absolute scandal".
He tweeted: "These individuals will not have had their contacts identified and those contacts may have become infectious and may have been spreading the virus."
Paul Hunter, professor of health protection at the University of East Anglia, said "there will be occasional glitches" in a system this size, but added: "I think the thing that surprised me was the size of it - almost 16,000 results going missing over the course of a week is quite alarming I think."
PHE said every single person who was tested initially had received their test result as normal, with all those testing positive told to self-isolate.
The number of call attempts to contacts of those affected is being increased from 10 to 15 over 96 hours.
Asked on Monday how many contacts of positive coronavirus cases had been missed as a result of the error, Mr Johnson told reporters: "I can't give you those figures. What I can say is all those people are obviously being contacted and the key thing is that everybody, whether in this group or generally, should self-isolate."
Shadow health secretary Jonathan Ashworth said the error was "shambolic", adding that "people across the country will be understandably alarmed".
