EDF may be subject to a multimillion-pound fine after many customers were left with no power for several days.
Industry regulator Ofgem is proposing to levy EDF with a £2 million penalty as punishment for leaving 100,000 customers without electricity and heat last year.
The outage was caused by a fire at EDF Energy Networks' Dartford Creek cable bridge in Kent on July 20th 2009, which resulted in the loss of domestic and business energy in 94,000 premises in the surrounding area.
A report into the issue by Ofgem found that the outage was out of EDF's control and that the company took the appropriate steps to limit the number of customers affected by the power loss.
However, the regulator said EDF did not take enough actions before the event to minimise the risk of an outage and will make its decision about whether or not to levy a fine in early August.
"As a minimum, we think that EDFE should have had a higher frequency of maintenance inspections and a higher level of security than was in place at Dartford Creek at the time of the fire," the report said.
If you want to find out more about your energy options and how you could save up to £378 in minutes, click here.