I just noticed on Sky News there now that Ryanair has said it is expecting disruptions and cancellations from 5 AM tomorrow morning. This is likely to happen all over Ireland (Dublin, Shannon, Belfast City, etc), north and south. It also says that part of the Scottish airspace has already been closed tonight.
Edit: Now the IAA has restricted all flights until 1 PM tomorrow, to and from Ireland, because of that ash cloud.