Everyone has been talking about how shocking Johnny Depp looks as renowned criminal Whitey Bulger in Black Mass – but what about how shocking Benedict Cumberbatch sounds?

The movie is based on true events surrounding Bulger’s reign of terror in Boston and his eventual switch to FBI informant in an effort to take down a mafia family who were invading his turf.

Cumberbatch’s fans are used to hearing his cut-glass British accent and his polite manners. But as the crime lord’s state senator brother, Bill Bulger, he sounds nothing like Sherlock Holmes, with a thick mobster-style drawl.

Depp cuts a sinister figure as Bulger in the film with thinning hair scraped back from his face and a deadly look in his eyes

Kevin Bacon plays FBI Special Agent Charles McGuire in the movie and the cast also includes Joel Edgerton, Jesse Plemons, Sienna Miller and Dakota Johnson.

The film is based on Boston Globe reporters Dick Lehr and Gerard O’Neill’s book Black Mass: The True Story Of An Unholy Alliance Between The FBI And The Irish Mob.

Johnny Depp as Whitey Bulger in Black Mass
Johnny Depp as Whitey Bulger in Black Mass (Warner Bros)

It will chronicle the life of the Boston crime kingpin-turned-fugitive Bulger, who rose to the top of the FBI’s Ten Most Wanted List after he went on the run for a decade. He was later captured in California in 2011 and is serving time in Massachusetts state prison for second-degree murder.

It is released in cinemas on September 25.