Ofgem's investigation into the power cuts on August 9 found that the combined loss of two large generators, and the smaller loss of generation at a local level, together triggered the disconnection, loss of power and disruption to more than one million consumers.
This included many commuters and rail passengers with traffic lights down and trains coming to a standstill.
It said on Friday that two large power stations, Hornsea One Ltd and Little Barford, did not remain connected after the lightning strike.
Hornsea One Ltd, co-owned by Orsted, and Little Barford, operated by RWE, have agreed to make a voluntary payment of £4.5 million each into Ofgem's redress fund, it added
The regulator also said that UK Power Networks had begun reconnecting customers without being asked to by the National Grid Electricity System Operator (ESO), which could have potentially jeopardised recovery of the system.
Ofgem said that UK Power Networks has recognised this technical breach, taken swift action to prevent any future re-occurrence and agreed to pay £1.5 million into its voluntary redress fund
Jonathan Brearley, executive director, said: “Consumers and businesses rely on generators and network companies to provide a secure and stable power supply.
“August 9 showed how much disruption and distress is caused to consumers across the UK when this does not happen.
“That is why it is right that companies that were unable to keep generating have paid into our consumer redress fund.
“Our investigation has raised important questions about National Grid’s Electricity System Operator, which is why our review will look at the structure and governance of the company."
Timeline of events which led to power cut - Friday August 9
4.52pm: Lightning strike on transmission circuit north of London, resulting in a small loss of generation
4.52pm: The lightning strike triggered two large generators to lose supply - Hornsea off-shore windfarm and Little Barford gas power
4.53pm: Back-up power is kept in the event of a outage, but only enough to cover the loss of the single biggest generator to the grid. However not enough to cover the scale of the loss of generation in this instance
4.53pm: At this point, the secondary back-up system kicks in and customers on this network experience an outage - around one million homes
4.57pm: The system returns to a "normal, stable state"
5.06pm: Power starts returning to customers
5.37pm: Distribution network operators return power to all customers, however there is an ongoing impact on customers
A report published on the same day into the incident by the Energy Emergencies Executive Committee unveiled Government-backed plans to strengthen the power network and make it more resilient to outages in future.
Business and Energy Secretary Andrea Leadsom has confirmed that the action plan will be implemented in full, to help prevent and manage future power disruption events.
She said: “The disruption caused to people and businesses by the power cut in August was unacceptable.
"However, customers can be confident that we have one of the most robust energy systems in the world and today’s report will help us reduce the risks of it happening again and ensure our energy sector is better prepared in the future.”