Public Health England has revealed that a technical issue with the UK government’s coronavirus dashboard led to 15,841 unreported cases.
With the sizeable shortfall now identified, the UK’s official recorded case figure for Sunday has leapt to 22,961.
“A technical issue was identified overnight on Friday, October 2, in the data load process that transfers Covid-19 positive lab results into reporting dashboards,” said Michael Brodie, the interim chief executive at Public Health England.
Mr Brodie said “rapid investigation” led to the identification of the missing cases and that most “occurred in most recent days.”
He tried to play down the incident and said all 15,841 people “received their Covid-19 test result as normal and all those who tested positive were advised to self-isolate".
Mr Brodie’s words are unlikely to ease the many critics of NHS Test and Trace.
The programme, led by former telecoms executive Dido Harding, has been subjected to sustained criticism over its inability to trace contacts and provide an adequate number of tests.
This has meant some of those requesting a test have been directed to centres hundreds of kilometres away.
The NHS Covid-19 app was finally launched last month after several false starts.
But the launch was not a smooth one as it soon became clear that despite its title the app does not link to the National Health Service.
Last week British Health Minister Matt Hancock said the app had been downloaded more than 12 million times, which represents under a sixth of the total population.