If you live in UK then UK contract with social security there. If you live anywhere else you'll get Irish contract with social security through Ireland. In other words, this should give you the right to state pensions in these two countries. Not a lot but it's at least something.
Possible additional tax and social security payments having to be made in your home country depending on where you live? As many already pointed out, pay is very low and I can't see many people jumping on this train.