The article seems to imply that RP is only used in England, or even specific to Southern England (though it discusses variant forms in Northern England), but I think accents very similar to RP are not unknown in Scotland and Wales among the upper social classes. (I do not know much about Ireland, but the 'Anglo-Irish' classes, in both North and South, in general seem to use RP.) In Scotland it is notorious that the aristocracy speak with an 'English' accent, supposedly as a result of an education in English boarding schools, but the practice seems to be somewhat more widespread, extending at least into sections of the 'upper middle' classes. Maybe someone with more knowledge of the subject could cover this?
I have come across this question, in various forms, many times and it is not easy to know how to reply. On the one hand, there is a belief that there are British people who, though born and brought up in Scotland, Wales or Ireland, are speakers of RP (as traditionally described and as spoken in the south of England). If there are such people, I think they are very rare. On the other hand, some writers have suggested that there are accents that can be called "Scottish RP", "Welsh RP" and so on - accents which display some characteristics of the regional accent implied by the name but are otherwise similar to English RP. This just seems wrong to me - an accent either is, or is not, RP.
Not that I like calling ANY accent RP!