Why is the Birmingham accent so difficult to mimic?

With a second series of Birmingham-set drama Peaky Blinders in the pipeline, the show's creator Steven Knight has admitted the city's accent is "very difficult to get right". What is it that makes it so hard to master, asks Brummie-accented Lucy Townsend. The accent frequently comes bottom in polls of people's favourites. It is rarely heard on television or in films unless they are comedies. It is