Martin Freeman returned to television on Tuesday night, but not as Dr Watson of "Sherlock." He appeared in FX Network's new anthology series "Fargo." This appearance is just one of the examples of how popular, and in demand, Freeman and Benedict Cumberbatch have become. And, according to media reports, the two successful actors' busy schedule is stalling the production of "Sherlock" Season 4.

BBC has yet to confirm that they have renewed "Sherlock" for Season 4, though the writing duo, Steven Moffat and Mark Gattis, have said that they have already plotted out the whole season four and season five.

The cast availability is turning out to be a major stumbling block. A spokesperson of the show has revealed that they are still in the conversation stage. "Conversations are still ongoing regarding Sherlock's return," the spokesperson said to Mirror Online. "Steven Moffat has already said that he has mapped out a fourth series, but it is always depending on cast availability."

"The last series was a fantastic hit for us and we're massively proud of the show," the spokesperson said, adding that everyone wants to start filming as soon as schedules permit.

Previously, Mark Gatiss had said to Metro, "Everyone wants to carry on doing Sherlock. It's a simple matter of schedules -- particularly Benedict and Martin."

The social networking site are buzz with news that "Sherlock" 4 is scheduled to premiere in 2016. According to a report, Freeman has confirmed the buzz, saying that it might take two years for "Sherlock" to return on BBC.

"Sherlock" returning after two years is something Gatiss had also alluded to in his interview with Metro. He had said, "There was suddenly a kind of outraged response that it might not be back until 2016 but that's precisely how long it always is. It's always two years! But we'd like to return soon, of course."

In one of his earlier interviews, Cumberbatch had almost confirmed that there are two new seasons of "Sherlock." However, it looks like his busy scheduled has made him change his tune. In a recent interview to Adelaide Advertiser, as quoted by the Radio Times, Cumberbatch said, "I genuinely don't know ["Sherlock" new season]."That's not me trying to be mysterious. None of us know if there will be a fourth, fifth or sixth series."