Wikipedia:
The full, official name, pound sterling (
plural:
pounds sterling), is used mainly in formal contexts and also when it is necessary to distinguish the United Kingdom currency from
other currencies with the same name. Otherwise the term
pound is normally used. The currency name is sometimes abbreviated to just
sterling, particularly in the wholesale financial markets, but not when referring to specific amounts; for example, "Payment is accepted in sterling" but never "These cost five sterling". The abbreviations "ster." or "stg." are sometimes used. The term "British pound" is commonly used in less formal contexts, although it is not an official name of the currency.
https://en.wikipedia.org/wiki/Pound_sterling#Names