When permission was granted for development of the airport, it was done so under the following condition:
Passenger and cargo fixed wing aircraft to be limited to the following types of aircraft, Jetsream 41, DHC-8Q400, ATR-42, ATR-72 and RJ146 or aircraft of equivalent characteristics in terms of size, weight, carrying capacity, noise and other polluting emissions.
While this may be changed at a later date, it rules out Ryanair ops initially.
EDIT: This was a condition of the 2013 planning approval, which was later overturned. I'm not sure if this clause was included in the final approval.