As a result, the system automatically disconnected customers on the distribution network - resulting in about 5 percent of electricity demand being turned off to protect the other 95 percent.
Jonathan Brearley, Ofgem’s Executive Director of Systems and Networks said:
"The power cuts of Friday 9 August caused interruptions to consumers’ energy and significant disruption to commuters. It’s important that the industry takes all possible steps to prevent this happening again.
"Having now received National Grid ESO’s interim report, we believe there are still areas where we need to use our statutory powers to investigate these outages.
"This will ensure the industry learns the relevant lessons and to clearly establish whether any firm breached their obligations to deliver secure power supplies to consumers."
Any breaches discovered in the investigation could lead to a financial penalty.
Ofgem also said it would be "looking at whether the companies made the right decisions both in the numbers of customers disconnected and whether those customers disconnected were the right ones".
Ofgem has launched an investigation into the National Grid power cuts after an initial report found that lightning was partly to blame for the blackout.
The probe will attempt to establish whether the parties involved - National Grid ESO, National Grid Electricity Transmission, 12* distribution network operators in England and Wales, as well as generators RWE Generation (Little Barford Power station) and Orsted (Hornsea) - breached their licence conditions.
On Friday, August 9, thousands of homes were left without power and people were left stranded on roads and trains when traffic lights and systems failed.
Although the grid was struck several times by lightning, this strike at 4.25pm was the only one to have a significant impact.
A lightning strike on a transmission circuit followed by "two almost simultaneous unexpected power losses" at the two power plants caused the blackouts.
The outages occurred independently and the scale of generation loss meant that the level of "backup" power required under the regulatory standards was insufficient to cover the loss, the report from National Grid Electricity System Operator said.