Ryanair yesterday declared it was "manifestly wrong" of the UK Competition and Markets Authority's (CMA) to refuse to review its 2013 ruling that the airline should cut its 29.8 per cent stake in rival Aer Lingus to 5 per cent.

The CMA’s predecessor, the UK Competition Commission, decided in 2013 that Ryanair should cut its stake in Aer Lingus partly on the grounds that it deterred other airlines from making a bid for the Irish carrier.

Ryanair challenged this in a tribunal and then in the British court of appeal, which in February ruled in the CMA’s favour. At that point Ryanair said it would carry on to the supreme court but also asked the authority to review its original decision on the grounds that circumstances had changed.

The request for a review was based on International Consolidated Airlines’ Group’s (IAG) €1.36 billion bid for Aer Lingus. Ryanair pointed out that the approach undermined the CMA’s claim that its stake in its fellow Irish carrier put off other potential bidders. The CMA provisionally ruled yesterday that circumstances had not changed and it was sticking with its order that Ryanair cut its Aer Lingus stake to 5 per cent.

Ryanair dismissed this yesterday, and said that ahead of the authority’s final decision on the review, expected next month, it would again explain why its original 2013 ruling should be amended to revoke the divestment order. In the meantime it will continue with its appeal against that original ruling.

However, some legal sources have suggested that the British supreme court may refused to hear that challenge as it dealt with the matter when Aer Lingus originally complained to the old UK Competition Commission. If this were to happen Ryanair can presumably fall back on the CMA’s decision to refuse to review its original finding, and launch a fresh set of appeals on the back of that.