Energy regulator Ofgem is to fine EDF Energy Networks £2 million for poor customer service, the watchdog said today.
The regulator said the firm had failed to offer connections quickly enough to households and businesses in more than 100 cases.
EDF distributes electricity to almost eight million customers in London and the East of England.
Sarah Harrison, Ofgem's managing director of corporate affairs, said: "Customers should not have to accept poor service in any part of the energy market."
EDF Energy Networks is a monopoly provider of certain connection services across the region.
In return for the costs paid by customers it is expected to offer good service and there is a back-stop three-month deadline for it to make offers for those seeking connection to the network.
But despite a warning from the watchdog in 2006, EDF Energy Networks failed to meet the deadline many times and did not have systems in place to judge if it was meeting the three-month rule.
The regulator said the company would have faced an even higher fine if not for the £450,000 in compensation it has already paid out to affected customers.
Ms Harrison added: "All energy companies should be in no doubt that, if they are failing to offer good customer service, Ofgem will take tough regulatory action.
"We recognise that EDF Energy has now taken steps to improve its connections service, but they should have taken this action some time ago."
The distributor is part of EDF, the French giant which bought nuclear power firm British Energy last year. EDF is also one of the UK's "big six" suppliers of gas and electricity.Reuse content