Oh well. Guess the brainteaser was either too hard or not interesting enough. Here are the answers anyway:
Anthony Higgins played the part of Sherlock Holmes in the TV movie Sherlock Holmes Returns. This was originally a pilot for a TV series, but it never got the green light. I actually quite enjoyed it though – you can probably find it on Five or Hallmark at some point.
As for the part of Moriarty, Higgins was Professor Rathe in Young Sherlock Holmes. At the end of the film, Rathe changes his name to Moriarty.
Jeremy Brett famously played Sherlock Holmes in a whole series of TV dramas from Granada, back when they still made quality TV. But he also played Holmes on stage in The Secret of Sherlock Holmes. The secret, it turns out, is that Moriarty and Holmes are the same person: Holmes has become so bored with his unchallenging cases that he’s developed an alter ego that is his own equal and therefore a challenge.
Anyone got any others?