Speedy’s Cafe, the sandwich emporium frequented by Holmes and Watson in the series, is a real café on Gower Street, near Euston – the BBC’s stand-in for 221b Baker Street. (In the Sherlock pilot it was run by Una Stubbs’s character and named Mrs Hudson’s Snax n' Sarnies, but that idea was swiftly dropped.) The fans who flock there from all over the world can now enjoy specially created Sherlock-themed snacks, specifically the Sherlock wrap (chicken, bacon, cheddar cheese, lettuce, peppers, red onion, cucumber, chilli sauce – all "wrapped up as tightly as Sherlock’s personality") or the Watson Wrap (roasted vegetables, spinach, tomatoes, spring onion, Brie, sour cream – "safe, warm, and comforting, like his personality").

5. Despite China’s best efforts, Sherlock isn’t gay

As amply demonstrated by the kisses in season three’s first episode, The Empty Hearse, Steven Moffat and Mark Gatiss have always enjoyed flirting with the ambiguity of Sherlock’s sexuality. "Everyone recruited him to their perspective, their interpretation," Benedict Cumberbatch once said when asked about Holmes’s sex life. "I’ve had asexuals come up to me and thank me for representing asexuals." But they’re mistaken, according to Moffat: "There's no indication in the original stories that [Holmes] was asexual or gay," he told The Guardian. None of which has stopped millions of Chinese fans from adopting Sherlock as a gay icon, with a vast archive of literature dedicated to his romantic exploits with Watson. There’s a 39-chapter romance novel; a much-viewed video super-cut of Cumberbatch and Martin Freeman (or ‘Curly Fu’ and ‘Peanut’, to give them their Chinese nicknames) exchanging longing looks set to slushy music; plus, of course, the inevitable S&M scenarios. All of which may seem like fairly standard fan-fiction fare – until you remember that in China, writing what the authorities consider filth is a crime punishable with a lengthy jail term.