Aer Lingus scored a hit against fellow Irish airline Ryanair in court today, which will allow British authorities to continue investigating the cheapo carriers over its ownership of a 30% stake in Aer Lingus.

This particular partnership is a touchy one, notes the Associated Press. Aer Lingus thinks Ryanair’s stake, built out of a hostile 2006 takeover bid that was blocked by regulators and the Irish government, is meddlesome and annoying. It wants Ryanair to be forced to sell the stake, because it’s a disruptive presence and doesn’t do consumers any favors.

Ryanair didn’t want the probe by Britain’s Office of Fair Trading into its status as No. 1 shareholder in Aer Lingus, as the investigation seeks to find out if the stake represents a threat to competition on British-Irish air services. Ireland itself owns a 25% stake in Aer Lingus, which Ryanair wants as well.

The Court of Appeal sided with the Office of Fair Trading and Aer Lingus, and Ryanair has said it would appeal that judgment.

Says Aer Lingus chief executive Christoph Mueller:

“It is unacceptable that our principal competitor has been allowed to remain as a significant shareholder on our share register even though the European Commission blocked their hostile takeover almost 5 years ago,” Mueller said. “This intolerable situation cannot be allowed to continue and today’s judgment confirms that the OFT has the jurisdiction to investigate the anti-competitive effects of Ryanair’s minority shareholding in Aer Lingus.”

Aer Lingus welcomes UK court victory over Ryanair [Associated Press]

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