Sherlock special set for Victorian London

The BBC teased an image of Benedict Cumberbatch and Martin Freeman in Victorian dress in November

The upcoming Sherlock special will be set in Victorian London, the show's co-creator, Steven Moffat, has confirmed.

Last year, the BBC released an image of Benedict Cumberbatch and Martin Freeman in character as the detective and his assistant in Victorian clothing.

It led fans to speculate whether the special would be set in the past, or if the pair were merely dressing up.

But Moffat told Entertainment Weekly it would be an historical adventure that stood alone from the main series.

"The special is its own thing. We wouldn't have done the story we're doing, and the way we're doing it, if we didn't have this special," he said.

"It's not part of the run of three episodes. So we had this to do it - as we could hardly conceal - it's Victorian."

Moffat added filming had been completed on the special and he was "very pleased" with the result.

The BBC has yet to confirm when it will be broadcast.

Meanwhile, Sherlock co-creator and star Mark Gatiss has said he based his character, Mycroft, on the British Labour Party politician Peter Mandelson.

"It was explicit even before I was going to play him," he told the Radio Times.

"Steven... and I talked about how Mandelsonian Mycroft was. Conan Doyle says Mycroft is the British government. He's the power behind the throne."

Gattiss is playing Mandelson for real in the new Channel 4 drama, Coalition, which airs on Thursday. 26 March.

The one-off special charts the turmoil that followed 2010's General Election, as the three main parties scrambled to form a coalition government.

It also stars Bertie Carvel as Nick Clegg, Ian Grieve as Gordon Brown and Mark Dexter as David Cameron.