7 Reasons Sherlock Series 4 Should Be The Last

So the use of Sherrinford would be problematic enough, but then there's the casting rumour. Tom Hiddleston is a terrific actor and he would undoubtedly do an excellent job between Cumberbatch and Mark Gatiss. But such blatant stunt casting would be symptomatic of a problem 'Sherlock' has been experiencing since the third series.

Unsurprisingly, the Internet was awash with theories as to how Sherlock survived the fall from the roof of St. Bart's Hospital at the end of series two. Steven Moffat even said that he looked at what fans were saying and incorporated them into the episode as fake-out hypothetical solutions. Which makes what happened next even more disturbing.

When Sherlock finally explains how he survived to Anderson, a character who went from sneering cynic to thinly-veiled piss take of a 'Sherlock' fan, the former forensics expert is disappointed. He then devolves into maniacal laughter and starts tearing at the news clippings plastered to his walls. And let's not get started on the feminist KKK gang that appeared in 'The Abominable Bride'.

For a man who claims to stay away from online criticism, Moffat knows exactly how to bait the die-hard fans. He obviously pays close attention to what Tumblr says about him and plays up to it, which some believe detracts from his scripts. For Moffat - who is an executive producer on the show and so has a say in every casting decision - to approve Hiddleston's casting would be a huge sign that he's stopped trying to write stories and is just using the series to vent his frustrations.