The British health system is the single most important issue driving opposition to Irish unification in Northern Ireland. Citizens of Northern Ireland get free medical care as part of the U.K.'s socialized medicine. British taxpayers subsidize Northern Ireland's public services to the tune of $12.5 billion, according to one estimate. That's a lot of money to give up for the nationalist cause. Nor is it clear more generally what the costs of unification would be or who would pay them, or what the economic benefits of unification might involve and who would get them.

It rubs my intuition the wrong way to believe that one form of socialised medicine over another is actually the major factor.  In any case, here is more from Kimberly Cowell-Myers.