In evidence to the House of Commons public accounts committee, NHS England chief executive Simon Stevens admitted that health service investigators had found an extra 12,000 items of correspondence that had not been processed or passed on to clinicians by the former provider of primary care support services, NHS Shared Business Services (SBS).
In addition, he told MPs, a handful of GPs were continuing to redirect patient data sent to them in error to the current centralised provider of support services - Capita - rather than returning it directly to the GP practice from which it originated. Around 150,000 items caught up in this process would need to be 'repatriated' to GP practices, he admitted.
One MP called the revelation that such a large additional cache of data had been identified - months after a comprehensive report on the problem by the National Audit Office was published - a 'bombshell'.
Mr Stevens told the committee that it remained the case that there was 'no evidence that any individual patients have been harmed' as a result of the health service's failure properly to manage the backlog of data. He said that the NHS aimed to work through the full backlog - both the original set of lost data and the newly-discovered batch - by the end of March 2018.
He NHS England was now taking 'a more cautious view' of how to handle the original 709,000 items unearthed. A total of 5,562 have now been deemed in need of a clinical review - up from just 1,788 highlighed in the NAO report in May.
'The vast majority have been done,' Mr Stevens told MPs. '4,565 have been completed, that means there are 997 of the original clinical reviews to complete by the end of December.'
Hundreds of these cases require a further clinical assessment to rule out harm to patients. Mr Stevens said: 'Of the ones that have been done, 3,624 have been clearly shown not to have relevant clinical detriment or harm, so there are 941 of that cohort awaiting final clinical review.'
Mr Stevens said that all of the new 160,000-plus records would be transferred back to GP practices by December, and that 'we should be gunning for the end of March' to resolve the issue completely. However, he admitted that if a high proportion of the latest batch of unprocessed correspondence was deemed to need full clinical review, that date could slip.
Committee chair Meg Hillier MP asked Mr Stevens if he thought the NHS had finally got to the bottom of the issue, or whether there could be 'another pile of data out there'.
The NHS chief told MPs that the whole data scandal had been uncovered as the health service shifted primary care support services from SBS and other local providers to Capita, and said that the service had become 'very rigorous in making sure we are lifting every stone'.
He added that the health service had recovered £4.3m from SBS to cover the cost of working through the backlog of data.