Published: 11:53, 20 August 2019
| Updated: 12:12, 20 August 2019
A lightning strike may have caused a recent major power cut in Kent, National Grid has claimed.
Following this announcement, government regulator Ofgem has launched an investigation into the incident to establish whether the utilities company breached their licence conditions.
More than one million homes across the UK were without electricity for around an hour on Friday, August 9.
In the preliminary report, National Grid states at 4:52pm there was a lightning strike on a transmission circuit in Cambridgeshire.
Immediately following this, two almost simultaneous unexpected power losses in Yorkshire and Bedfordshire occurred independently of one another - but each associated with the lightning strike.
The company said it is not abnormal for lightning to hit the electricity grid, and it happened several times that day.
But the combined power loss to the network was greater than the backup capacity held in case of emergency.
In this instance, 5% of Britain's electricity demand was turned off to protect the other 95%.
This "extremely rare and unexpected event" has not happened in more than a decade.
National Grid said power was returned to all customers by 5:37pm.
But Ofgem wants to establish whether there was sufficient back-up power to manage the loss of generation supplies.
"It’s important the industry takes all possible steps to prevent this happening again..." Jonathan Brearley, Ofgem
It will also look into whether the right customers were disconnected.
A number of other generation and distribution companies are also being investigated to check they met their obligations.
Jonathan Brearley, Ofgem’s executive director of systems and networks said: "The power cuts of Friday, August 9 caused interruptions to consumers’ energy and significant disruption to commuters.
"It’s important the industry takes all possible steps to prevent this happening again.
"Having now received National Grid'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."
However, Ofgem has highlighted the investigation does not imply National Grid has done anything wrong at this point.
More by this authorRebecca Tuffin