Sherlock won’t be back for a while (Christmas 2015, we're expecting) – but when it does return, it could be all change according to the series’ creators.

“The show has to keep evolving, it has to move on at a pace, I think,” says producer Sue Vertue, wife of writer Steven Moffat.

Vertue’s not the only one with her eye on the future. “What we want to do for a fourth series is match [series three],” says co-creator and star Mark Gatiss, speaking in an interview on the special features for the upcoming series three special edition DVD, “but it’s not a question of saying ‘Well we need a baddie on that scale [of Charles Augustus Magnussen].’”

“It’s about trying to find stories that have that kind of scale to them.”

The BBC drama blockbuster returned to great fanfare earlier this year, with the mystery of Sherlock’s (Benedict Cumberbatch) apparent suicide solved and John Watson (Martin Freeman) getting married.

However, some fans objected to the series’ shift in focus from crime-solving to character comedy/drama – but Gatiss and co-creator Moffat (who also runs Doctor Who) believe that the strength of the series lies precisely in this area.

“An episode needs to be about something in their lives,” Moffat said. “It is not enough for it to be a mystery.”

“It is a series about a detective, it is not a detective series,” agreed Gatiss.

“The mystery of the week is as nothing compared to the relationship between those two characters and their increasingly large family of characters. That’s the real heart of it, and that’s why it’s a success.” 

The debate will doubtlessly rage on – but no matter what makes Sherlock a hit, Moffat and Gatiss say they’d be happy to continue doing it as long as they can.

“The idea, if we could, of finding Martin and Benedict in those chairs aged 50, sort of like the age that Holmes and Watson are usually portrayed... is sensational,” said Gatiss.

“It would be lovely to feel like we could do that.”

Sherlock will return with a Christmas special in 2015