Brussels — The European Commission plans to open an in-depth investigation into the UK power capacity market promptly, despite appealing against the EU Court of Justice ruling requiring it to do so, an EU source said late Tuesday.

UK power capacity market auctions and payments due to companies have been frozen since November, when the ECJ General Court ruled that the EC had failed to examine the UK's capacity market in enough depth before approving it under EU state aid rules.

"Since the UK intends to maintain the measure, the commission will take the necessary steps to open an in-depth investigation...as required by the court," the source said.

The EC has in parallel appealed the ruling in a bid to have it overturned, the ECJ confirmed Tuesday.

"The decision to appeal does not put on hold the opening of such an in-depth investigation," the source said. "The commission understands the importance of a prompt resolution of this matter for the market."

The appeal is not likely to resolve the issue quickly, with appeal decisions taking on average a year or more, according to the ECJ.

The EC will announce it has opened the investigation once it is underway, the source said.

-- Siobhan Hall, siobhan.hall@spglobal.com

-- Edited by James Burgess, newsdesk@spglobal.com