Variations of English are spoken around the world but, for the most part, English is English.
The Idiom Attic lists several categories of idiom that were coined in a specific country, for example Idioms of American origin or of Australian origin. Idioms that originated in Britain aren't displayed as a separate list because there are so many of them.
So much of the English language originated in the UK, or more exactly England, that, if an origin isn't given as somewhere else, you can be reasonably sure that it is British.
For instance, most proverbs were first heard in their English form in England, likewise phrases coined by writers of the Bible, the works of Shakespeare, nautical language and much more.