Is The Emerald Isle still snake-free? I would think in this global age it would be nigh to impossible to keep stowaways, pets and souvenirs out of the country. The introduction of snakes has been devastating to the ecosystems of other islands. Has Ireland managed to fend of serpentine invaders?
In Britain, the Adder is heavily endangered, and the (IIRC) two other indigenous species are also in decline. Ireland’s climate and habitat would be just about sufficient for the Adder, but various man-made circumstances would prevent a population to establish itself. And in any case, nobody keeps them as pets. The species which are kept are pretty much incapable of surviving outside anywhere in the British Isles, certainly not enough to establish themselves.