In July 2007, it became illegal to smoke in enclosed public spaces and shared workplaces in the UK. That, as they say in Doctor Who, is a fixed point in time. You can now tell in an instant whether a book, film or a TV show made in this country is set before or after that date, simply by noticing whether the characters, if they smoke, go outside to do so.

Smoking used to be significant, especially on film and TV. It is now even more so. At first, it was a prop; famously, or so it was said, a way of giving actors something to do with their hands. I prefer to think that it is a way of expressing, or evading, some deep inner turbulence. It signifies nonchalance and its opposite, while providing for the camera and our gaze a curling backdrop of smoke with which the cinematographer can make play.

Consider the difference between a speech made without the exhalation of smoke, and one made with it: words are made visible, the mouth issuing smoke signals as the lips open and close. (The most extraordinary example of this that I can think of, incidentally, takes place in a film set before tobacco smoking became a global habit. In John Boorman’s Excalibur, Helen Mirren’s Morgana exhales what look like cubic kilometres of smoke as she summons the dragon’s breath for her witchcraft. I wonder how they did it.)

The effect can only be replicated by filming in the cold, and that can be tricky to arrange if your film is set in, say – to take a not entirely random example – Casablanca. That is the smoking film par excellence, and it has been argued by Richard Klein, in his excellent book Cigarettes Are Sublime, that the fug in which it is bathed adds greatly to its emotional clout, and prompted Franklin Roosevelt’s 1943 meeting with Churchill and De Gaulle – in that same city. (Not a notion that bears too much scrutiny, but it is pleasing to entertain.)

Nowadays, you can’t just smoke and get away with it, can you? Actually, you can, in a way. The opening episodes of Mad Men hinged on an ad campaign for Lucky Strikes, and people smoked in that series as if it was going out of fashion. This may have indicated inner moral corruption, but golly, didn’t it look good? Smoking now expresses defiance, a snook cocked at authority. The recent adaptation of Len Deighton’s SS-GB had so much smoke in it that even I started coughing – and I’m a smoker. Shot as it was in half light, this made visual sense: smoke makes the murk in which the characters operate even murkier; and what better way to annoy a Nazi occupying your country – for Hitler hated cigarettes – than to smoke? As for the health risks of smoking (smoking being a lightning rod for righteous disdain), who’s going to care about living longer when you could be rounded up by the Gestapo?

The most famous smoker in literature is Sherlock Holmes. (Although one would like to acknowledge PG Wodehouse’s Bertie Wooster, who appears to chain smoke his way through the Jeeves stories, often, if memory serves, starting even before breakfast; certainly, his post-breakfast cigarettes are an unbreakable ritual for him.) Holmes, in the books, would get through three pipefuls of cheap, nasty shag tobacco if he was wrestling with a particularly knotty case; but he also smoked cigarettes, a fact ignored by every portrayal of the detective until Jeremy Brett’s unimprovable rendition; I can still recall the weird, fastidious way in which he held his gaspers. (Compare the unusual way in which Austro-Germans would hold their cigarettes, whether you’re Erich von Stroheim in real life, or, on film, any of the non-British officers in the earlier scenes of The Life and Death of Colonel Blimp. Nothing visually says “foreign” quite so much as a cigarette held between the middle and third fingers.)

Benedict Cumberbatch had fun with his nicotine patches – “this is a three-patch problem”, etc – but you can see how he could not quite be allowed to smoke an actual cigarette. His not-actually-smoking Holmes can, in the very exercise of withdrawal, be seen to be undergoing an extra torment, a further tension for an already tense persona. But there is an interesting point about the smoking ban in relation to films in which we do see real people smoking real cigarettes in banned spaces. The ability of actors to smoke in films and on TV is among a short list of exemptions under the 2006 Health Act that instituted the ban. Screen inhalation now gives the habit a charge it never had.