Benedict Cumberbatch has admitted that he first thought taking hit show Sherlock back to the Victorian era for a one-off special was “madness”.

In the New Year’s Day episode, Sherlock Holmes and companion John Watson (Martin Freeman) will haunt the eerie streets of London in the year 1895 to solve the case of The Abominable Bride.

Sherlock
Benedict Cumberbatch as a Victorian Sherlock Holmes (BBC/Hartswood/Robert Viglasky)

But Benedict had reservations about the time travel.

“I thought it was madness. I thought (the writers) had finally lost the plot, jumped the shark, all the other cliches of television gone mad with itself.

Sherlock
Benedict and Una Stubbs (BBC/Hartswood/Robert Viglasky)

“Then they expanded the idea and pitched it to me properly and I think it’s fantastic. Absolutely brilliant,” he said.

News that the episode would be turning back the clock first leaked from fan photos on set, but Benedict said he still had no idea how fans will react.

Sherlock
Martin Freeman returns as Doctor Watson (BBC/Hartswood/Robert Viglasky)

This special will be the first new Sherlock episode in nearly two years so unsurprisingly expectations are high.

“I don’t really know how the fans are going to react to it. I think that’s one of the joys of doing it like this… We haven’t disappointed fans in the past it seems so hopefully this won’t.”

Luckily, reaction from fans so far – to images of Benedict and Martin in their Victorian clothing and the first full-length trailer – has been fervent.

Sherlock
Rupert Graves is the owner of beautiful sideburns as Inspector Lestrade (BBC/Hartswood/Robert Viglasky)

The clip saw Sherlock – hair slicked back compared to his usual curly mop – and a moustachioed Watson hurtling through the back streets of London, stumbling across gruesome murders and coming face-to-face with threatening new foes.

And regardless of whether we enjoy it, Benedict made it clear he had plenty of fun filming it, citing Martin’s comedy chops as one of the best things on the set.

“Great fun to play, and I mean, great, great fun,” he said. “To muck around with a pipe and a deerstalker for real is wonderful.

“And then, as far as the background goes, the setting, the mise en scene, the scenery, all the rest of it, it’s just a delight. It always is with period drama. You kind of marvel at it.”

Sherlock
Amanda Abbington is back as Mary Morstan (BBC/Hartswood/Robert Viglasky)

Returning too will be Amanda Abbington, who plays Watson’s wife Mary Mortstan, and Una Stubbs as landlady Mrs Hudson, although little is known about what roles they’ll have in the plot.

The Abominable Bride is not one of Arthur Conan Boyle’s stories but is inspired by a case mentioned briefly by Watson in the 1893 short story, The Adventure of the Musgrave Ritual.

Sherlock
The eponymous ‘Abominable Bride’ (BBC/Hartswood/Robert Viglasky)

According to writer Mark Gatiss, who penned the script with Steven Moffat, the story is “a full-blooded Victorian Gothic”.

In an interview with The Independent, Benedict added that going back to the world of Arthur Conan Doyle’s was “easier” than playing the modern version – a man who is meant to be “slightly out of his time”.

Sherlock
Tim Barlow in an unknown role as Wilder (BBC/Hartswood/Robert Viglasky)

“You feel some of the weight is taken off you. You’re no longer trying to establish this man in the 21st century.

“The other gorgeous thing about going back in time is that you can actually look to the books for source material, which I always do for our version anyway, but it’s even more qualifiable to lean on them for inspiration,” Benedict said.

But have no fear, the modern day Sherlock will return and Benedict said he’s still “pretty determined” to make time in his packed schedule for the show.

Sherlock
Benedict says he wants to continuing doing Sherlock (BBC/Hartswood/Robert Viglasky)

“I’m still enjoying it. We’ll see how the next series goes, but I’d love to keep ageing with him. It would be an interesting experiment to do.

“Martin and I started this relatively young compared to other Holmes and Watsons, so why not?”

The Abominable Bride will air on January 1 on BBC One.