'The Hobbit' star plays Dr John Watson in the cult hit, sidekick to eccentric sleuth Sherlock, played by Benedict Cumberbatch, in the modernised TV adaptation of Conan Doyle's classic detective stories.
Dedicated fans make pilgrimages to the sandwich shop featured in the show outside Sherlock's home and the spot on the pavement where Sherlock apparently "died" at the end of the last series, and filming on the latest episodes has seen the cast dogged by crowds of fans with cameraphones as they try to shoot on location in London.
Martin told Empire magazine: "The reaction to it has been unlike any I've had to any other job I've done. I've got some great reactions to things I'm very proud of, but I don't think any surpass Sherlock in terms of critical acclaim and numbers of people watching - and just a general feeling that you're in a mini Beatlemania."
The actor is sworn to secrecy about what writers Steven Moffat and Mark Gatiss have in store for the next series, but he admitted they all felt under pressure to live up to the hype.
He said: "We had a lot to live up to after the last run. Every time we do it we want to make something better and not rest on our laurels, which would be very easy to do."