If you ask people what they think British English sounds like, most would probably mention the Queen, or Harry Potter at the very least. However, across the British Isles there is a massive variety of accents and dialects....
Take a trip round the UK and Ireland one accent at a time with this Accent Map of the British Isles : accent-map.expedia.co.uk/
British English vs American English pronunciation
British accent vs American accent
Here's a compilation of American Actors portraying British characters: from Angelina Jolie, Gwyneth Patrow to Johnny Depp
Here's a compilation of British Actors portraying American characters.
Top 10 Awful American Accents By Non Americans: from Orlando Bloom, Colin Firth to Jason Statham