The head of NHS Test and Trace has assured there was no risk to patient data during this month’s Excel error.

Responding to parliament’s science and technology committee, Baroness Dido Harding said there was “at no time any risk to patient data”, adding that it is kept securely “in line with data protection regulations”.

The committee wrote to Harding on 8 October asking for clarification on whether the decision to use Microsoft Excel to hold Covid-19 test data breached statutory or regulatory requirements for safety.

In her response published on 16 October, Harding said a new system had been commissioned to replace the “legacy system” but failed to address whether the use of Excel had breached regulatory requirements.

“This new system is currently being built and will be assessed as part of our winter readiness plans,” she wrote.

It comes as nearly 16,000 Covid-19 cases went unreported between 25 September and 2 October, reportedly due to an error with a Microsoft Excel spreadsheet.

Public Health England (PHE) developers reportedly used an old file format known as XLS, which can only handle about 65,000 rows of data. When the spreadsheet reached its maximum size, it prevent new cases from being added to the file.

The glitch resulted in efforts to trace thousands of contacts of those who tested positive being delayed.

Health secretary Matt Hancock told MPs on 5 October that the incident was being “investigated fully”, confirming that a decision to replace the “legacy system” had been made in July.

“The technical issue was not caused by the use of an old format. Rather, PHE have confirmed that there was a failure in the process for preparing some testing data for uploading onto the central system that stores all test results,” Harding said in her response.

“A rapid mitigation has been put in place by PHE working together with NHS Test and Trace that splits large files and a full end to end review of all systems was immediately instigated to mitigate the risk of this happening again.”

She confirmed that increased testing meant some Excel files used to transfer data exceeded their file size, preventing further data from being uploading.

Harding has faced calls to “consider her position” as head of NHS Test and Trace due to the missed cases, coupled with some of the lowest Test and Trace figures reported.