Are Northern Irish banknotes valid everywhere in the UK?

Okay, let's talk about Northern Irish banknotes. It's true that they are valid throughout the UK, but it's a bit more nuanced than that. You see, unlike Bank of England notes, which are legal tender, banknotes issued by Northern Irish banks (and Scottish banks, for that matter) are technically promissory notes. This means the issuing bank promises to exchange the note for legal tender – which is Bank of England money. Now, while shops and businesses *can* refuse to accept them, they are generally accepted across the UK. The key thing to remember is that acceptance is at the discretion of the retailer. So, while you might occasionally encounter someone unfamiliar with Northern Irish notes, leading to a refusal, they are indeed valid and circulate throughout the UK. It's a quirk of the UK's banking system, reflecting the historical independence of Scottish and Northern Irish banking institutions.