Sherlock Holmes is a national treasure, a literary character who has long enjoyed "untouchable" status. He arouses especially strong passions among the purists who feel deeply possessive about "their" man. Mess with him at your peril.
So the makers of Sherlock Holmes and the Case of the Silk Stocking, BBC1's radical new take on their hero, may be diving for cover after the film goes out on Boxing Day. Ian Hart, who plays the sleuth's companion and chronicler, Dr John Watson, in this new Holmes story written by Allan Cubitt, is certainly bracing himself for some flak from Arthur Conan Doyle devotees.
In his trailer during filming in the East End of London, Hart says with a twinkle: "I hope this will offend the purists. They are looking back at Holmes and not really seeing him for what he was. His stories were popular fiction knocked out in 10 minutes for quick-turnaround serialisation.
"We revere Shakespeare, but he too was changing things all the time, adding topical gags. Now we say you can't change a word of his. It's the same with Conan Doyle. He's constantly been altered by successive generations. The deerstalker and pipe were not mentioned at all by Conan Doyle; they were added by the illustrator." Hart played Watson in BBC1's The Hound of the Baskervilles two years ago.
The scene I'm witnessing is one that may raise hackles. We're on the set of a Victorian opium den. All around the dingy interior lie slumbering figures who have clearly partaken of the narcotics on offer. A Chinese man packs a hookah with drugs and lights it. The camera pans along the pipe before coming to rest on perhaps the most celebrated aquiline profile in English literature. The addict closes his eyes, leans back on his silken pillows and exhales with a contented sigh; Sherlock Holmes is blissed out.
Playing up the detective's drug habit is just one way in which the film departs from the "authorised version". Rupert Everett in the title role is another, but he's an inspired casting. With sharp eyes and a stern gaze, and at an imposing 6ft 4in, he brings natural hauteur and authority to the role of the famed resident of 221B Baker Street.
Everett evinces a spry, almost camp sense of humour usually absent from more po-faced depictions of Holmes. He also brings to life the detective's razor-sharp intelligence. In this story, Watson has been away and Holmes has not seen him for six months. Yet as the doctor approaches his old friend from behind in a peasouper, Holmes knows who it is. "Morning, Watson," he says, without turning round.
"Holmes, how did you know it was me?"
"You reek of the slaughterhouse - eau de mort."
Everett explains that Holmes's drug addiction is just one piece of the complex emotional jigsaw he's trying to portray. He wants to render the detective as less "vaudevillian" and more psychologically cogent. "This character is so well known that in the past, no one has felt the need to explain why, say, he doesn't like coffee. Past portrayals have just never gone inside his head. If someone is a drug addict, I want to know why he is a drug addict. It's obvious that something is haunting Holmes, which he needs to take his mind off.
"In this version, there is no politically correct moulding of the drama to show him ticking himself off - 'Naughty me, I should never do drugs!' But I think it's interesting to try to find out why he takes drugs. Has he seen too many decapitated heads? I find that sort of psychological examination of the character fascinating."
Dark episodes in Holmes's past might also help to explain why he is, according to Everett, "a diva. He's very difficult to control, a law unto himself. He's just not used to anyone telling him how to behave. He thinks he's right about everything, even though in this story he makes two or three enormous mistakes - which is why he needs Watson with him. No one else understands Holmes's flaws in the same way."
Elinor Day, the producer, chips in that the film-makers have set this story a bit later than usual to give Holmes a more contemporary feel. "We've set it in 1902, the dawn of a new age. Characters such as Watson's psychologist fiancée, Mrs Vandeleur [Helen McCrory], bring in fresh ideas, such as Freudian theories. Procedural detection was moving on with the introduction of such techniques as fingerprinting and psychological profiling. Those details allow us to shift the Holmes legend into a world audiences today will recognise."
This drama, which centres on a serial killer targeting high-society debutantes, also removes those two most iconic of props - the deerstalker and the pipe. The director, Simon Cellan Jones, wants to get away from hackneyed interpretations of Holmes, as epitomised by Basil Rathbone's "stiff upper lip" portrayals in the movies of the 1940s.
"Don't worry: it's not a hip-hop Holmes," Cellan Jones says. "We didn't want to take too many liberties, but we did feel it was important to dispose of clichés like the pipe and the deerstalker and make it utterly un-caricatured. Every generation should be allowed to have a go at Sherlock. He's one of those eternal characters, like Hamlet or Lear, who can bear any number of interpretations. We're determined not to make this Holmes feel fusty and old-fashioned."
This Watson will also be very different from previous portrayals as a pedestrian, even buffoonish, sidekick. Hart plays him as Holmes's intellectual equal. "We're a more sophisticated audience, and we're less ready to accept that Watson is utterly stupid. He has qualified as a doctor - you can't play him as a complete moron. He must be pretty intelligent to understand Holmes's methodology and present that information to the public. Previous films have depicted Watson as some kind of halfwit."
Hart contrasts the dark edginess of this film with the more bland tone of most telly 'tecs. "There are too many detectives on the TV - and yes, I know, we're about to add to their number. But the fact is that viewers like TV detectives. So, while solving crime is familiar to viewers, what's different here is the style in which it's done. Sherlock Holmes making clever use of words doesn't happen in The Bill."
Everett believes that the Holmes character has endured so robustly because there in an inbuilt sense of British tradition in him. In Cellan Jones's view, "he is a timeless character who works in any period. He's like James Bond; he's lasted because everyone who reads the books or watches the films would love to meet him and be liked by him. He's a very rewarding friend."
In addition, Hart says, Holmes can be whatever we want him to be. "He's such an alluring character because he's mysterious; you never quite know who he is. There's so much room for your own interpretation because he's so ill-defined. You can go anywhere with that character.
"I'd like to go very high camp with him - I've got tons of ideas for Sherlock Holmes musicals. Or I'd like to have him as a kind of Zelig character, cropping up at key points throughout history. And the Great Train Robbery would never have happened because Holmes would have been sitting in the last carriage."
Above all, though, we are drawn to Holmes because he is just not like the rest of us. "Sherlock Holmes is an expression of what we'd all like to be," says Hart. "He sees things that no one else sees."
'Sherlock Holmes and the Case of the Silk Stocking' is on BBC1 at 9.25pm on Boxing Day