A few notes on terminology: Great Britain is a geographic term, not a legal one. Great Britain is an island divided between England, Scotland and Wales which all, along with Northern Ireland, form the United Kingdom. The demonym of United Kingdom, confusingly, is "British". Sometimes "Great Britain" is used to specifically refer to the UK without Northern Ireland, though there are plenty of parts of England, Wales and especially Scotland that are also not on Great Britain.
Anyway, to answer your question: the currency of the entire UK is Pound Sterling, which is the same everywhere: £1 in London is the same as £1 in Edinburgh. Some Banks in Scotland and Northern Ireland have permission from their respective devolved governments to print their own banknotes, but they must be backed by Bank of England notes stored in a vault and, importantly, they are not automatically accepted elsewhere. Some large retailers will accept them, but shops in Northern Ireland, England and Wales are under no legal obligation to accept a Scottish banknote, whereas the Bank of England notes are accepted everywhere.
Also, while the banks that issue notes in Northern Ireland and Scotland are just regular, privately-owned commercial banks, the Bank of England is entirely publicly owned and doesn't offer much in the way of traditional commercial banking services.
Oh, shit, right, so I get to share something I learned fairly recently.
For much of human history, wealth could be measured many ways but by far the most powerful currency was land. Land meant resources, and the land's value was determined by what respirce it produced: fertile floodplains meant crops, lakes for fishing, forests for hunting, and, worst-case scenario, moorland could be used for grazing livestock. But what if that wasn't enough? What if you had huge tracts of land but your narcissism and insecurity were so overwhelming that you just needed to prove yourself even more?
Enter: lawns. Lawns are fields of grass, which is a useless crop that can only really be used for grazing. But the grass is kept so short that livestock can't graze on it. But grass like that can only be grown on plains that are ideal for crops, so you need to get rid of the crops. And short grass needs tending, tending with more care than any crop, so you need to have workers dedicated to it. That's what a lawn is: it's bragging, it's saying "not only do I have loads of top-quality land and an army of workers, I can afford to piss away huge swathes of it for absolutely no reason other than to prove that I can." It's hard to image a greater and more grotesque display of boujee excess than the lawn.
Of course, this is what makes the modern lawn all the more pathetic: that neatly parcelled-out vast tract of land you can afford to squander as a display of your immeasurable wealth is, like, a few meters across. It's like the Stamford apes experiment: they know what they must do, but not why they're doing it and, if they knew what a lawn really was and where it came from, I can't imagine many would be quite so attached. Then again, maybe they would be. Maybe they really do think their home is a castle and that they live in a kingdom they can walk around in thirty second.