Sounds like your rental property in west cork isn't really a rental property at all? It's a second home for yourself that's rented out for a few weeks a year? So the mortgage interest would probably not be deductible in this case, but the rental income would be taxable. That's what it looks like to me based on what you have said.
Sounds like you need to talk to a professional... If you don't mind me asking, why are you getting into rental property investment without knowing how it works financially?