Sherlock writer Mark Gatiss adds to speculation show could be over due to Benedict Cumberbatch and Martin Freeman's packed schedules

The Sherlock writer, co-creator and actor, Mark Gatiss, has added to speculation that the phenomenally successful BBC drama may have run its course.

He stated that it was a growing challenge to find time when both the main stars, Benedict Cumberbatch and Martin Freeman, can film together.

"I honestly don’t know if there will be any more. It’s incredibly difficult to get Benedict and Martin’s diaries to align," Gatiss said at the WhatsOnStage awards, according to The Sun.

"And obviously we left it in a very happy place… If that’s the end I’d be very happy where we left it."

The fourth series ended on Jan 15 with a particularly dark episode featuring Sherlock's long-lost sister. It left fans around the world wondering whether the team would return for a fifth series.

Gatiss also revealed the final day of filming had ended with a “whimper”.

“The last day tends to be an odd day—it’s never quite as you imagine it. But we did actually try and contrive it so the very last shot was Benedict and Martin running out of the building," he said.

“Then we realised that we had to do one last shot the next day of Martin falling over — so that’s how it ended. As usual these things end with a whimper.”

Cumberbatch has said of whether the hit show would return: “We never say never on the show. I’d love to revisit it... but in the immediate future we all have things that we want to crack on with and we’ve made something very complete as it is."

Last week, Cumberbatch's Sherlock was named the world's favourite BBC TV character.

Sir Arthur Conan Doyle's fabled spy beat competition from acclaimed British television figures, including Basil Fawlty, the Doctor in Doctor Who and Hyacinth Bucket, to take the accolade.

BBC Worldwide surveyed more than 7,000 18 to 64-year-olds from seven countries including Australia, France, the US and Japan in the public vote, with almost 30% backing Cumberbatch's Sherlock.

In second place was the Doctor, while Idris Elba's murder detective DCI John Luther came in third.

Cumberbatch also took the crown for most memorable scene as Sherlock for his apparent fall to death at the end of the show's second series.

It was named most iconic BBC moment with 26 per cent of the vote, ahead of Monty Python's Dead Parrot sketch in second.

Colin Firth's Mr Darcy emerging topless from the lake in Pride And Prejudice also made the top 10 in fifth while David Brent's improvised dance at a comic relief party in The Office came in eighth.

Cumberbatch said: "I'm honoured to hear that my portrayal of Sherlock has been internationally recognised as viewers' favourite BBC TV character.

"Who would have thought a high-functioning sociopath could be so popular with people all over the world?"

The contemporary reimagining of Conan Doyle's Sherlock, co-starring Freeman as Dr Watson, has been sold by the BBC to 240 territories internationally.

The series, created by Gatiss and Steven Moffat, has received numerous accolades since its debut on the BBC in 2010.