> In most countries of the world the issue of banknotes is handled exclusively by a single central bank or government, but in the United Kingdom seven retail banks have the right to print their own banknotes in addition to the Bank of England; sterling banknote issue is thus not automatically tied in with one national identity or the activity of the state.

https://en.wikipedia.org/wiki/Banknotes_of_the_pound_sterlin...

For instance if I were to go further south, any Scottish notes I have would not be accepted in a load of places. More generally using banknotes from Northern Ireland in Britain will get you funny looks and a near 100% refusal.