According to BBC News, we are lending Ireland 7 billion at 5% and borrowing it at 1 1/2%. So we make 25 million per year as long as it remains unpaid.
It doesn't mention any payment protection insurance, though. So if it goes unpaid, we will have no comeback, other than taking Ireland to court and getting a county court judgement.
And they will probably be told to pay it back at a pound a week.
