Regulator is examining if EP SHB and SSE Generation billed the grid too much to cut their production levels
Ofgem is investigating two companies to find out if they overcharged the grid to lower their production levels.
The energy regulator said it was looking into whether EP SHB, which owns the South Humber Bank gas power plant, and SSE Generation broke the terms of their licences in a way that could have ultimately pushed up household energy bills.