How would A citizen of the R. of Ireland go about joining the British Army?

Im 17 years old and living in Spain. I want to join the Irish Defense Forces but as always the�re not recruiting....plus to be honest, I don't find the IDF as attractive as the Regular Army in Britain. So the thing is my parents are all like ohhh the british army will treat the Irish as s ect ect abuse ect thus if I turn around to them now and say that I want to join the Brit Army they will probably not help or sign papers. What should I do? What should I say to them?