Energy regulator Ofgem has accused npower of producing a "misleading" report about the cost of producing gas and electricity.
The firm had argued that rising costs of transporting energy meant they could do little to control the prices charged to consumers.
Npower had released documents claiming those transportation costs would increase by around 20% by 2020, but Ofgem said the data was "incorrect and misleading".
More top news
Net long-term migration to the UK is at its lowest level for three years, latest figures show.
The remains were discovered by Malaysian forces helping the search of the USS John S McCain's flooded compartments.
Testing has shown large variations in the time taken to sound in British Standard-approved fire alarms, with one failing to go off at all.