OFGEM has launched an investigation into National Grid and Scottish Power Transmission over the Western high-voltage direct current (HVDC) subsea cable.
The Western HVDC is a £1.3 billion subsea cable that transports electricity between Scotland, Wales and England.
The project was undertaken by a joint venture between National Grid Electricity Transmission and SP Transmission.
The investigation will review the performance of both companies in delivering the cable.
It will consider whether its late delivery means they breached special licence condition 6I, which specifies the expected delivery date of the cable.
Additionally the investigation will consider compliance with standard licence condition D (provision of transmission services) and section 9(2) of the Electricity Act 1989 (provision of economical, efficient and co-ordinated services).
The investigation will also examine potential breaches relating to the operation of the cable.
A spokesperson for Ofgem said: “The opening of this investigation does not imply that we have made any findings about non-compliance by National Grid Electricity Transmission or Scottish Power Transmission.”