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While it's the inner workings of renowned detectives that impresses the most, our favourite fictional investigators often have a penchant for uncompromising hairstyles and face furniture. Obviously, the greatest of them all has to be Agatha Christie's Hercule Poirot, described by the author as "a little man with enormous moustaches" in Murder on the Orient Express, and Kenneth Branagh's recent movie versions have featured the character's most outrageously sculptured examples yet.

Tom Selleck as the gloriously mustachioed Magnum PI.

Surely the brainy Belgian can only be bettered in the hairy upper lip stakes by the great Magnum PI, the 1980s Hawaii-based detective played by moustache hero Tom Selleck (a recent Magnum reboot featured an actor with a nude upper lip and so will not be considered). True Detective's Ray Velcoro, as portrayed by Colin Farrell, had an impressive Magnum-esque 'tasche of his own, while his partner Rustin Cohle (Matthew McConaughey) went for the droopy Yosemite Sam look. And, of course, there's the great(ish) Inspector Clouseau.

Moving upwards, several private eyes have sported memorable hairstyles, including Ace Ventura's bizarre quiff, Modesty Blaise's frequent colour changes, Charlie's Angel Jill Munroe's much copied, highly layered seventies-tastic look (with Farah Fawcett pulling off a 'Jennifer Aniston' long before Jennifer Aniston did) and Cadfael, who was landed with the rather severe, monk-favoured tonsure look.

So does the notable hair help? Obviously the supreme skills of the famously un-hirsute Kojak blows this theory out of the water.

A disregard for the rules

Sometimes the great sleuths have to bend the rules to get to the bottom of a case. Detective Chief Inspector John Luther, as played by Idris Elba, has actually developed a finger blister due to the number of times he has torn up the rule book.

Clint Eastwood's 'Dirty' Harry Callahan didn't get that sobriquet due to his personal hygiene habits and Lisbeth Salander from Stieg Larsson's Millennium series is angry, antisocial, violent and quite heavily (not to mention, dragonily) tattooed. John Constantine (played by Keanu Reeves in the movie version of the comic book) is known to summon demons to solve his occult cases. Jim Rockford of The Rockford Files was an ex-con (for a crime, remember, that he didn’t commit) who often shied away from convention to get his man.

Perhaps the most egregious rulebreaker is Dexter Morgan from Jeff Lindsay’s Dexter book and TV series, who is not only a blood-splatter analyst but also a part-time serial killer dispatching other murderers that he’s not too fond of.

If you think of words 'detective' and 'hat' then only one name springs to mind: Sherlock Holmes. Where, or who, would he be without his distinctive deerstalker, described, adorably, by author Conan Doyle as an "ear-flapped travelling cap"? But Holmes is not the only famous investigator to don some iconic headgear.

Joan Hickson as Miss Marple in 麻豆社 One's 4.50 from Paddington.

Ann Cleeves's Vera, as portrayed by Brenda Blethyn, wears a somewhat unflattering bucket hat (reportedly purchased from a market stall in Newcastle) which is not a million miles away from Miss Marple's floppy straw hat, especially in the 1980s 麻豆社 Joan Hickson iteration. GK Chesterton's Father Brown often has a Catholic priest's cappello romano perched on his ecclesiastical dome.

Hardboiled gumshoes such as Philip Marlowe and Sam Spade would not be seen dead without a distinctive trilby, as did the slightly suaver French detective Maigret. The fashion forward Benoit Blanc from the Knives Out film series has also been known to enjoy a pretty snazzy dark navy velvet smoking cap with silver embroidery.

Other strings to their bows

All great detectives need a distraction after a hard day of investigating, and some have particularly bespoke hobbies to help them unwind. Inspector 'Tequila' Yuen from John Woo's ultraviolent Hard Boiled movie enjoys playing the clarinet when he isn't shooting guns. Other famous musical prodigies include Sherlock Holmes with his violin and Lord Peter Whimsy and his piano, while Ian Rankin’s Detective Inspector Rebus has an extensive vinyl record collection.

Inspector Morse is good at crosswords, Columbo is a master of foreign languages, Poirot grew vegetables, PD James's Adam Dalgliesh wrote poetry, Sara Paretsky's VI Warshawski enjoyed a spot of karate and Charles Paris would occasionally indulge in acting, when not investigating thespian-based crimes.

And the legendary Nancy Drew appeared to excel at everything as, according to one of the many anonymous Drew authors, she painted well, spoke French, drove expertly, was a great tennis player and "danced like Ginger Rogers". I mean, that's just showing off.

Every great detective needs a catchphrase.

Columbo always uttered "just one more thing" before trapping his suspect, while the John Thaw version of Inspector Morse was forever yelling "LEWIS!" at the top of his lungs.

Poirot often used his "little grey cells" to unmask a murderer.

Hawaii Five-O's Detective Steve McGarrett constantly implored Danno to "book 'em".

Joe Friday from Dragnet insisted on "Just the facts, ma'am" and Kojak tended to say "Who loves ya, baby?" for no clear reason.

Sherlock Holmes was known to declaim that "the game is afoot!" (quoting Shakespeare, no less), but his most famous catchphrase, "Elementary, my dear Watson", never appeared in any of Conan Doyle's books.

He was known to say 'elementary' and 'my dear Watson' on separate occasions, so putting them together in his many later incarnations probably just seemed, well, elementary.

You can hear an array of famous detectives in action by listening to 麻豆社 Radio 4 and 4 Extra's Whodunnits collection here.