Ryanair has been ordered to cut its stake in rival Irish airline Aer Lingus to just 5 per cent.
The UK Competition Commission is investigating the budget airline's 29.8 per cent shareholding in Aer Lingus to see if it is preventing that carrier from merging to remain competitive.
The commission today unveiled its final report, which concluded Ryanair's shareholding could "substantially lessen" competition on routes between Ireland and the UK, and told it to slash its stake to 5 per cent.
Ryanair said it would appeal the commission's findings.
CEO Michael O'Leary said: "The report by the UKCC is bizarre and manifestly wrong but also entirely expected."
O'Leary's comment comes a month after Ryanair vowed to unconditionally sell its stake in Aer Lingus to any EU-based airline in an attempt to appease the Competition Commission (see news, July 23).
Ryanair has tried three times to take over its Irish competitor - the latest attempt was blocked by the European Commission in February.
Aer Lingus chairman Colm Barrington said: "Today's final report by the UK Competition Commission confirms that the minority shareholding in Aer Lingus held by our closest competitor is anti-competitive and contrary to the interests of the approximately 14 million passengers who fly on routes between the island of Ireland and Great Britain.
"It was unacceptable that our principal competitor was allowed to remain on our share register with a shareholding of 29.82 per cent and interfere with our business despite the European Commission blocking both Ryanair's first hostile takeover attempt six years ago and its most recent hostile takeover attempt earlier this year."