Lionel Wigram is "working on" a new 'Sherlock Holmes' film.

Robert Downey Jr.

Robert Downey Jr.

The film producer has revealed he has come up with "a really good idea" for the third instalment of the series alongside actor Robert Downey Jr. - who plays the protagonist in the films - and his wife, director Susan Downey, having previously brought the detective to the big screen with 2009's 'Sherlock Holmes' and 2011's 'Sherlock Holmes: A Game of Shadows'

He said: "We're working on it. I think we have a really good idea, a good concept for it, and we're working on it with Robert and Susan and everybody. We've had many, many meetings and we have a really good writer who is engaged."

However, the filmmaker - who is currently working on film adaptations of 'The Man from U.N.C.L.E.' and 'Fantastic Beasts and Where to Find Them' - is still trying to hammer out the plot and won't make it unless the storyline is "fantastic".

He continued: "We're still trying to crack the story together. For us, if we're going to do a third 'Sherlock Holmes', it has to be fantastic, so we have to be really confident that we can give the audience a story that makes them say, 'Wow, this was worth it, this was better than the last two.' So that's what we're trying to do. I think we have a concept that cracks that, that gives the potential for that, so now it's about how do we get the other stuff to make that work?"