allowed to fly over Irish airspace.

There are a few issues with that, Leo:

The legal:The right to fly over Irish airspace is guaranteed by a treaty to which Ireland is a signatory and which has nothing to do with the EU
The economic: The damage to Ireland's economy and access to Europe from such a move would be much, much greater than that to the UK's
The practical: There is literally no means of enforcing this. Ireland's airspace is only guaranteed by the protection offered by the RAF, since Ireland has no air-to-air combat capability and what combat aircraft it has couldn't even reach a commercial airliner, let alone keep up with it. Presumably, Leo envisages that we will maintain our defence of his country's airspace while having our aircraft banned from it?

Grandstanding fvcking clown.