If one of your grandparents is an Irish citizen who was born in Ireland, but none of your parents was born in Ireland, you may become an Irish citizen. You will need to have your birth registered in the Foreign Births Register.
Have just been looking this up, and annoyingly my Dad never registered as a foreign birth so I'm shit out of luck. Unless my fiancé applies and then we're married for 3 years. Probably won't have £231 left by that point though...
http://www.citizensinformation.ie/en/moving_country/irish_citizenship/irish_citizenship_through_birth_or_descent.html
Does Irish = Norther Irish in this context?