leftover Irish Pounds

or you could have spent the Irish pounds paying for your last night in Ireland or a taxi or bought breakfast/lunch/dinner in the airport. Or you could bring home a souvenir from the airport paid with cash. You'll always get more for your cash when you spend rather than exchanging it for other currencies.

Same holds true with Euros

I’ve never understood why foreign exchange dealers refuse to accept Northern Ireland (and Scottish) sterling banknotes. Maybe they are just stupid?

Irish pounds have not existed in over 10 years, Ireland is on the Euro

Are you not likely returning to Europe for future travels? Most people save their leftover Euros for "next time".

Northern Ireland and Scottish banknotes are not legal tender by law. They have been issued up to an amount of legal tender on deposit with the Bank of England as allowed by law. Similarly, Bank of England notes are not legal tender in Northern Ireland or Scotland (only coins issued by the Royal Mint are) also by law. However, most places in the UK will accept any of the bank notes for payment.

Since the Irish and Scottish notes are not legal tender, there is no reason a currency exchange outside the UK that deals only in legal tender would accept them.

You could always sell them to a friend or relative taking a trip to the UK if you get stuck with them.

http://edu.bankofengland.co.uk/knowledgebank/what-is-legal-tender/

I’ve no idea what the very narrow technical term of legal tender has to do with foreign exchange dealers, but they are losing business by refusing to accept sterling banknotes - so I still think they are stupid.

Ultimately, the only value any currency has is the willingness of others to accept it.

If anyone has any First World War First Issue Bradbury Treasury Notes don't accept 92% of face value from "Left Over Currency" as even in fairly poor condition they can be worth 100 times face. They must be having a laugh listing things like this ... unless they are fishing for someone coming across great-granddad's collection.

"the only value any currency has is the willingness of others to accept it."

You stated the exact reason. Currency exchanges simply have no willingness to take the Irish and Scottish bank notes. There are other examples from around the world where the notes are perfectly valid while in the country but have no value outside the country and the exchanges refuse to take them.

I would buy them from a friend if I was planning a trip to the UK. I know I can spend them there.

Northern Irish and Scottish notes are easy to forge so that is why a lot of places won't accept them. If in England they can easily be exchanged for English notes. English notes are accepted all over the UK.