Seong-Jae Kong, known as Korean Billy on YouTube, took an interest in UK’s diverse dialects during his year as an exchange student in University Lancashire. On returning back to South Korea, he started a YouTube channel of videos explaining the differences between the varying dialects in Britain. Soon enough, he gained a huge following in both the UK and South Korea on YouTube. 

Korean Billy copies accents and explains phrases to educate his viewers in his videos as well. Here's an earlier introduction to the British dialects:

And here is a more recent video of him comparing pronunciations in American English vs British English:

What do you think of his accents? Are they pretty spot on?