Meanwhile, Sherlock producer Sue Vertue has hinted fans could be treated to longer series in future, although episodes will stay true to their original 90-minute format.
She told Collider.com: "You might not always have three episodes. The [unaired] pilot was 60 minutes. But... we shot it again and made the pilot 90 minutes. Since then, it's always been 90 minutes.
"You might not always have three, possibly ... but they'll stay that length. It's a good length, I think."
Two more series of Sherlock - which also stars Martin Freeman as Watson - have currently been commissioned.
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