Within the UK, different accents and dialects exist. Received pronunciation is often referred to as the Queen’s English or BBC English, which is estimated to be spoken by approximately 2~3% of the British population.
Some would argue that RP is outdated, but this couldn't be further from the truth. Many aspiring British actors learn RP at acting school, and it is spoken by many famous and notable people within the UK. Check out these Pinterest links to get an idea of British people who speak RP in some form or another.
Some would also distinguish between the traditional, upper, neutral, and modern forms of RP. For example, perhaps the younger members of the royal family, such as Prince William, could be considered to speak with a more modern RP accent.
There is no "correct way" to speak English, however received pronunciation would be suitable for non-native English speakers since it is clear and tends to be easily understood by others. Those who need to communicate clearly and effectively, such as diplomats, businessmen, interpreters, and scientists, would probably benefit from learning RP.
More information about what Received Pronunciation is can be found here: https://en.wikipedia.org/wiki/Received_Pronunciation