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

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?''