I got an international driver's license, cost 30 something zloty, took a couple of days and is valid for 3 years.
It gives a list of countries where it is valid, which includes Britain and Ireland.
I'm guessing that if you have an (e.g.) U.S. driver's licence you can get this international one and drive in Ireland etc...
It's an A5 paper sized paper book with your photo glued in and stamped over.
Only in Polish, which is a little strange as you can't use it in Poland but hey, when in Rome, show them Polish...
Międzynarodowe prawo jazdy
Anyway, I probably didn't need it but the countries I need are listed and some of the countries are very very bureaucratic, so better safe than in jail.