WHEN British Prime Minister David Cameron undertook an official trip to China in December 2013, one question bothered the locals he met above all others: why can't you persuade the BBC to make more episodes of Sherlock?
That gives us an indication of the stature of a show that could, without much fear of contradiction, now be described as the most popular drama in the world.
Aired in 240 territories across the globe, Steven Moffat and Mark Gatiss's modern-day reworking of Sir Arthur Conan Doyle's timeless detective stories has scooped 12 BAFTAs, seven Emmys and a prestigious Peabody Award. It has netted no fewer than 76 gongs around the world.
As if that wasn't already enough proof of what an international hit the show has become, the global Sherlock Facebook page now has more than five million fans. Oh yes, and the Korean pop group SHINee have recently released a single entitled Sherlock, inspired by the BBC drama.
That popularity is underlined the day The Independent is on set in central London watching the filming of the fourth series.
We are hemmed in behind portable metal barriers outside "221b Baker Street" (in fact, the nearby North Gower Street).
Next to us stand thousands of Sherlock aficionados, who have travelled from every corner of the globe to catch a glimpse of their heroes, Benedict Cumberbatch (who plays the title role) and Martin Freeman (Sherlock's steadfast companion, Dr John Watson).
The fans are rewarded when Cumberbatch miraculously materialises from a side street - and is greeted by the sort of uninhibited cheering usually reserved for the stands at Wembley Stadium. Stopping to chat to people on the other side of the barrier, he is unfailingly polite to the legions of followers who track every move of the production on a website called "Setlock".
The actor, who is as charming and personable as his alter ego is detached and aloof, sits down with The Independent in a neighbouring hotel before filming to talk through all things Sherlock.
He begins by considering why, more than a century after this unorthodox "consulting detective" first appeared in print, he still remains such a widely adored figure.
According to Cumberbatch, 40, "he's such an iconic character. He's been loved worldwide for the last 129 years. There is something very peculiar and eccentric about him that makes him essentially English and absolutely universal at the same time. He is the most filmed literary character of all time. It's a lot to live up to. No pressure, then!"
So in a suitably Sherlockian manner, let us try to deduce the reasons why this particular version of Conan Doyle has chimed with audiences everywhere. Moffat thinks the casting of the two central characters is key.
"We've probably got the moment on tape. Among several Watsons, Martin had a chance to audition with Benedict. The moment we saw them acting together for the first time, we knew that was the show right there."
That chemistry between the two leads is what continues to make this iteration of Sherlock so compelling. Cumberbatch affirms that. "People just love the relationship between Sherlock and John.
"They're both very self-aware and affectionate, but also very truthful with one another. There are a really complementary team. John humanises Sherlock, and Sherlock gives John a shot of adrenaline and adventure and the chance to live a life less ordinary. That's a very potent combination."
Parts one and two of Sherlock season four are available to stream on Stan now.
Sherlock: The Final Problem streams on Stan from Monday.