IT has emerged that the systems failure which led to around 16,000 positive Covid tests disappearing occurred on software made obsolete well over a decade ago.

Public Health England was using Microsoft Excel XLS files to log cases south of the Border.

Created in 1987, this file type was made obsolete by the introduction of XLSX files in 2007.

Whereas an XLS file can handle around 65,000 rows of data per template, an XLSX file can hold over one million.

While this wouldn’t have prevented the error which came as a result of using Excel and not professionally made database software, using XLSX files would have at least delayed it until testing was significantly higher.

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Professor Jon Crowcroft, from the University of Cambridge, told the BBC: "Excel was always meant for people mucking around with a bunch of data for their small company to see what it looked like.

"And then when you need to do something more serious, you build something bespoke that works - there's dozens of other things you could do.

"But you wouldn't use XLS. Nobody would start with that."

Public Health England said 15,841 cases between 25 September and 2 October were left out of the UK daily case figures as a result of the error.

This meant that England’s daily cases were unreported significantly, which may have affected decision making about further lockdown measures.

Also, the positive tests were not logged in the track and trace system, meaning not one of those cases had their close contacts investigated.

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Yesterday, the number of positive cases who had not been contacted was still at over 5000.

The revelation will put further pressure on the English Health Secretary, Matt Hancock, who has refused to discuss the fiasco or explain why modern software was not used.

Hancock told MPs the weakness in the “PHE legacy system” had been found in the summer and contracts for a new system awarded in August - but did not say why it had not yet been replaced.

PHE is reportedly still using Excel, and dividing the cases into smaller chunks so as not to repeat the mistake.