Why do we say GBP instead of UKP?
I was torn between posting this here or on finance SE. I feel it's more likely to get useful answers here, if you disagree please comment.
It is common for the UK pound (£) to be referred to as GBP, which I feel safe in assuming stands for "Great Brit(ain|ish) Pound"
But Great Britain does not include Northern Ireland, indeed the full name of the United Kingdom is "The United Kingdom of Great Britain and Northern Ireland" which makes that pretty clear.
Since NI uses the same pound surely it would make sense to refer to the currency as UKP rather than GBP.
My assumption would be that the term GBP was coined before NI became a member of the UK in 1922 but I cannot find any evidence to support this.
Can anyone confirm if this is the case? If so, why was it never changed? It's been nearly 100 years now...
If my assumption was wrong, what other reasons are there that we do not refer to it as UKP?
"GBP" is a written convention used in exchange markets and a few other places. We don't "say" GBP.
GBP does not stand for "Great Britain pounds" or "Great British pounds", and neither of those phrases is correct or idiomatic. The currency is referred to as "the pound", "the British pound", or "the pound sterling".
Wikipedia says:
The ISO 4217 currency code is GBP, formed from "GB", the ISO 3166-1 alpha-2 code for the United Kingdom, and the first letter of "pound". It does not stand for "Great Britain Pound" or "Great British Pound". Occasionally, the abbreviation "UKP" is used but this is non-standard because the ISO 3166 country code for the United Kingdom is GB
UK v GB
"UK" is normally the abbreviation for "United Kingdom", but as Wikipedia observes, "GB" is the ISO code for the United Kingdom. It is also used as the international vehicle registration code. It is actually the UK's country domain (.uk) that is the odd one out in terms of international codes, although:
.gb is a reserved Internet country code top-level domain (ccTLD) for the United Kingdom.
UK / Britain / Great Britain
You write:
My assumption would be that the term GBP was coined before NI became a member of the UK in 1922
I don't know when it was coined, but before 1922 the inaccuracy would have been even greater, since the country was then the United Kingdom of Great Britain and Ireland, i.e. the whole of Ireland was part of the UK.
Of course, many writers over the centuries have treated "UK", "Britain" and "Great Britain" as synonyms (the same is traditionally true of "England" to a large extent - George Orwell regularly used "England" to mean the UK, and Shakespeare referred to England as an "isle"; this usage of "England" is no longer considered acceptable in the UK, but remains widespread fairly outside the UK). Today, the term "British" is still widely used to mean "of the UK" (including by the UK government, e.g. https://www.gov.uk/world/embassies ; https://www.gov.uk/becoming-a-british-citizen ), and "Britain" is often used to refer to the whole UK ( http://www.nationalarchives.gov.uk/cabinetpapers/themes/korea-entry-britain-war.htm ). These usages of "Britain" and "British" are generally considered acceptable. "Great Britain" is more likely to be reserved for geographically accurate usage, although not always (especially in older works).
This has nothing to do with the English language: GBP is an international code: ISO 4217
In 1973, the ISO Technical Committee 68 decided to develop codes for the representation of currencies and funds for use in any application of trade, commerce or banking. At the 17th session (February 1978), the related UN/ECE Group of Experts agreed that the three-letter alphabetic codes for International Standard ISO 4217, "Codes for the representation of currencies and funds", would be suitable for use in international trade.
ISO 4217 is a standard published by International Organization for Standardization that defines alpha codes and numeric codes for the representation of currencies and provides information about the relationships between individual currencies and their minor units.
The ISO just wanted some simple codes - I doubt that there was much argument about any of them.