CSC and NHS Connecting for Health have taken more than a month to restore patient data systems to the local service provider's primary datacentre in Maidstone.
Hospitals in the North West and the West Midlands had been running from a CSC back-up site after a major datacentre outage at the end of July left them unable to access core systems for up to four days.
Multiple failures left 72 primary care trusts and eight acute care trusts without access to patient administration systems.
A root cause analysis of the circumstances leading up to the power outage highlighted that "unusual individual technical factors combined to produce the power outage and associated equipment failure".
CSC said it regretted the failure and "has already put actions in place to ensure that such an incident cannot occur again".
Connecting for Health said it would be revisiting its service level agreements with CSC following the failure.
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