Andrew Scott's performance as Sherlock super-villain Moriarty was so good, and the character so well received by fans, that even after killing him off with a self-inflicted bullet through the brain at the end of season two, the show's co-creators Mark Gatiss and Steven Moffat couldn't resist finding new ways to give him cameos.

He featured in the multiple fake solutions to Sherlock's death-defying fall at the start of series three, and in the season finale, asking from beyond the grave "Miss me?", not to mention a number of appearances in Sherlock's Mind Palace, and then extended flashbacks in series four.

Given that weight of evidence, perhaps it's no surprise that when asked whether he has any regrets about creative decisions made on Sherlock, Gatiss admitted "There’s always things you’d do differently. Maybe we shouldn’t have killed Moriarty off in the second season..."

Speaking during an interview at the Oxford Union, the writer added "I remember going to the Edinburgh TV Festival with Andrew Scott and he said ‘I’m a bit sad really because it’s all over’ and he’s left the show, like, five times now.

"That was the point though – telling 90-minute stories, they’re so big and film-length the stakes [like killing off major characters] have to be big."

Does Gatiss have any other regrets about Sherlock?

"Give me 20 years to decide – by which time there’ll be a fifth season…”