Sherlock's Steven Moffat has confessed he is worried Benedict Cumberbatch and Martin Freeman will become too famous to star in the show.
Steven co-created the TV adaptation of Sir Arthur Conan Doyle's famous detective with Mark Gatiss and since it launched in 2010 Star Trek's Benedict and The Hobbit star Martin have gone on to become massive Hollywood stars.
Steven told The Sun: "It's a problem by accident and design. We do have two of the biggest film stars in the world playing the leads in our show. But they seem to like doing it and we hope we can hang on to them for a bit."
The third series of the BBC One detective drama begins filming in March and will be broadcast in the autumn.
And writer Steven admits he is struggling to juggle the show with preparing for Doctor Who's 50th anniversary in November.
He joked that his workload is "hell", adding: "But it's hell in a lovely way because I'm working on my two favourite shows - Doctor Who and Sherlock.
"Not a completely unbiased choice but it is very difficult.
"There's a lot to do. I'm a bit anxious and scared about getting the Doctor Who 50th wrong - but I think it's going well."