E.ON has been told to pay £7 million to the Carbon Trust for its "unacceptable" failure to supply enough advanced meters to business customers, regulator Ofgem has revealed.

The energy giant will also face a sales ban and a further £7 million redress if fails to meet its new interim targets.

Ofgem said the advanced meter roll-out was part of a national project to modernise the energy sector and provide better service by introducing next-generation, smarter meters to help customers control their usage and bills.

Suppliers who failed to deliver on time are nonetheless still required to roll out advanced meters, the regulator said.

Anthony Pygram, Ofgem senior partner with responsibility for enforcement, said: "It is unacceptable that E.ON failed to roll out advanced meters to these business customers on time.

"Customers have lost out on receiving better information about their energy consumption and the opportunity to control costs. Unless E.ON improves their poor record, they will have to pay out even more and may face a sales ban.

"The roll-out of advanced meters has the potential to transform the energy market. We expect all suppliers to learn the lessons from this ahead of the domestic smart-meter roll-out, in particular the need to start the process in good time and ensure senior managers are committed to delivering on time."

E.ON was not immediately available to comment.