The writer told PA: “There’s certain things about The Adventure of the Empty House which feel set in stone because that’s how Sherlock comes back, but at the same time we feel free to invent and to introduce new stuff to it. I always found it a little unlikely that Dr Watson’s only reaction was to faint for instance – as supposed to possibly a stream of terrible swear words.”

Gatiss added that he and co-creator Steven Moffat will continues to take a “magpie approach” when choosing which of Sir Arthur Conan Doyle’s original stories to use as inspiration.

He commented: “Everybody has their favourites, Steven and I have our all-time favourites, but it’s really a question of what will fit into the structure. We’re sort of guided by our idea for the overall feel of the next three stories.”

Earlier this week PBS exec Rebecca Eaton told Collider that “there will only ever be three [episodes] at a time, if we’re lucky”. She explained: “It’s getting harder and harder to do another season, not just because Benedict [Cumberbatch] and Martin [Freeman] are getting such high profiles, but Steven and Mark are busy and in demand.”

Moffat revealed earlier this year that the long gaps between each series are likely to continue: “…the way it works with Sherlock is that we starve you and then we give you a short burst and then we starve you again. It’s worked so far, we’re not going to change it.”

Executive producer Beryl Vertue has stated that filming on the third series will begin in “early 2013”.

Are you looking forward to Series 3? Let us know below…

> Order the BBC’s new official book, Sherlock: The Casebook, on Amazon.

> Buy the Series 1-2 boxset on Amazon.

Watch a clip from the Series 2 finale…