Some years back, I was attending a conference in Taiwan, listening to a senior Taiwanese scholar present on the Received Pronunciation (RP). It is roughly the same as "BBC accent" or "posh Southeastern English accent". The presenter said only 1% of the British population spoke with such accent. And yet he recommended it be taught to learners in Taiwan. So, during the Q&A session, I asked: If there are so few people using it, why should we teach it? Then my boss sitting next to me covertly reminded me that it was impolite to ask questions to senior presenters during Q&A sessions, so I backed off.
And to answer this question now myself, I think there is still a value in exposing learners to the RP, even though it's a dying (?) accent in England.
Even though RP has long lost its prestige in England, it is still widely taught to "foreigners", especially in Europe. So you are likely to come across a second-language speaker of English with an RP-inspired accent. In Hong Kong, Singapore, India and other Anglophone countries in Asia (with the exception of the Philippines), the teaching model at schools still derive from the RP. But many Taiwanese learners, especially those at lower proficiency levels, are quite unfamiliar with anything other than the idealized General American pronunciation. So they find it rather hard to understand second-language speakers who have learned British English back in their home countries.
Despite the fact that its speakers are considered "affected" and "cold" within the UK itself, the RP is a well-documented accent. There are many dictionaries and ESL textbooks that use this pronunciation, including authoritative ones like Daniel Jones's English Pronouncing Dictionary. Those are handy for teachers when they are not sure about pronunciation. On the other hand, most American dictionaries don't prescribe any one particular pronunciation. The phonetic symbols they use are designed to allow room for variation. Although language is and always will be varied (and that's the beauty of it), but that's not necessarily a comfortable situation for teachers looking for something "definitive". (Especially so for "non-native" teachers, who feel insecure for their perceived lack the authoritativeness as an authentic source of English.)
Plus, the RP has retained its prestige, in out of all places, America. I've seen many TV programs, commercials and movies where (fake) posh British accent is used for some supposedly positive effect. Even though very few people in Britain actually speak like that, Americans seem to associate it with some kind of fancy/fanciful European stuff. So if you are thinking of going to America, having an RP sort of accent might help. I must add though, that this might not apply if you are not European. My experience is that some Americans are not as favorable to non-whites with a British-derived accent. Maybe they notice you look like a foreigner and have an "unusual" accent, so they just conclude that you have a "foreign" accent. (Across the border in Canada, though, I notice that some people expect "foreigners" to be taught British English, even if their own variety is so much closer to that of the US.)
But in the context of Taiwan, all I'm saying is we should expose learners more to different accents including the RP, which is quite useful because it's taught to international learners. I'm not saying that they should all try to sound like the Queen with an exaggerated "aristocratic" intonation. Don't do this all the more if you are going to the UK. There, people with regional working class or black accents are considered cool nowadays. I'm saying that you will find it becomes easier for you to understand people from many different countries speaking English, once you are familiar with what they are being taught at school: the RP.
