According to this, Britain still uses pounds and Ireland should be using euros.

However, here, they are telling me that I'm going to be very, very confused when we get there because they officially use the Irish punt, which I've never heard of (I should've taken my history and geography classes a bit more seriously when I was in high school...), but as the punt's worth seems to vary a hell of a lot, they say a few businesses welcome sterling. That's two. However, they say the euro is being introduced in Ireland, so most shops display two prices for each item. This is con.fu.sing.