Sherlock star Andrew Scott has revealed that cast and crew members have been banned from discussing the plot details of the next series with their loved ones.

Andrew, who plays Moriarty in the BBC One show, told the Mirror that while he had had a ‘fantastic’ time filming the forthcoming episodes, he couldn’t say any more about them.

“If I told you what happens they would kill me,” he said. “It has been fantatsic filming the new series but we have all been banned from telling our families and friends what is in the scripts.

“We are not allowed to speak to anyone.”

The second series of Sherlock ended on a cliffhanger as Benedict Cumberbatch’s title character, wrongly accused of being a killer, plunged to his apparent death from a rooftop.

The ending has left fans speculating for months over how the detective might have faked his demise – given that Benedict is back on board for series three, suggesting Sherlock is in fact alive.

Andrew added that he has been taken aback by how popular the show has become.

“I don’t think everyone thought it would be so successful,” he admitted. “I can see it still on TV in 20 years as we all started working on it when we were very young.”

A transmission date has yet to be confirmed for the next series, which went into production in the Spring.