In April 2008, Ofgem launched an investigation into allegations that Scottish Power abused their dominant market position relating to the electricity transmission network they own jointly in Scotland. Ofgem said it had launched its inquiry into Scottish Power and SSE under section 18 of the Competition Act, "based on a formal complaint alleging abuse of a dominant position in the electricity generation sector arising from constrained capacity on the transmission network." The energy regulator believes that energy generators manipulate the power market for profit when supplies are tight because network operator National Grid has to pay utilities to turn their plants on or off to balance supply and demand. This resulted in companies deliberately shutting their plants down when supplies are tight in order to receive a higher payment to start up again, increasing the system balancing costs at the expense of consumers. Ofgem was alarmed that the cost of balancing the system increased from £70 million in 2007/08 to an estimated £238 million for 2008/09 and an expected £258 million in 2009/10, with most of the costs incurred in Scotland. In January 2009, Ofgem suspended the investigation, saying it would be more effective to deal with the wider problem than pursuing the specific case further.