There have been further indications that the European Commission, which is due to announce a decision tomorrow on Ryanair's landing rights deal at Charleroi Airport in Belgium, will find that the arrangement was illegal.

RTÉ News understands that the commission's ruling will describe the discount deal as a 'secret commercial contract'.

Ryanair receives a 50% discount on standard landing charges at Charleroi. It is expected the European Commission will rule that this arrangement and how it was agreed was illegal.

It is also expected to rule that the 15-year contract between Ryanair and Charleroi should be restricted to three years.

The commission is also expected to rule that any grants received by Ryanair from the Walloon government will only be permitted if they can be linked to the cost of setting up new routes.

It is understood the commission will not put a specific figure on the amount Ryanair may have to repay the Walloon government. This will be negotiated, but estimates vary between €4 and €10 million.

Decision to govern future rules

The decision by the commission will deal specifically with Charleroi but it is likely to form the basis of future rules governing how publicly owned airports offer incentives to attract airlines.

In a separate ruling, the Competition Authority in Ireland is expected to issue a finding today that Aer Rianta did not operate its support scheme in a transparent way.