The game's afoot, and has been, at increasing speed, since about 1860. Whodunnit? When it comes to the art of detection, we all do it. We have been doing it since Victorian times, and will continue to, because the contest between criminal and sleuth has become a sort of cultural religion.

The detective novel is the quintessential British literary genre, embodying two of our most cherished national characteristics: a faith in reason and a suspicion that our neighbours, respectable as they may seem, are no better than they should be. These twin aspects are wonderfully evoked in Kate Summerscale's The Suspicions of Mr Whicher, deserved winner of this year's Samuel Johnson prize for non-fiction. The book re-examines a famous Victorian murder: the killing in 1860 of three-year-old Saville Kent in Road Hill House, Wiltshire, the home of a well-to-do and apparently upright factory inspector.

The story inspired William Wilkie Collins and Charles Dickens; its influence can be traced though Sherlock Holmes, Miss Marple, the board game Cluedo and a thousand modern strands of detective fiction.

Jack Whicher, the grim and grizzled investigator sent by Scotland Yard to solve the Road Hill House murder, is the direct ancestor of inspectors Poirot, Morse and Rebus, and of every amateur armchair detective poring over clues in the latest media mystery, from the disappearance of Madeleine McCann to the murder of Meredith Kercher.

Times Archive, 1860: The recent murder at Road-hill House

A crime has just been committed which for mystery, complication of probabilities, and hideous wickedness is without parallel

• Leading article: Road child murder

• The case of Constance Kent

• Constance Kent indicted

The first fictional detective was Edgar Allan Poe's Auguste Dupin in 1841. In 1866, the French writer Émile Gaboriau created Monsieur Lecoq, based on the real-life François Vidocq. Today, every nation has its own literary sleuth: Henning Mankell's Kurt Wallander in Sweden; Boris Akunin's 19th-century Russian Erast Fandorin, a posse of US gumshoes and squads of Italian detectives, private and police. There is even Matteesie Kitologitak, an Eskimo detective with the Royal Canadian Mounted Police, in the novels of Scott Young.

Yet the genre remains distinctively British, even when transposed to distant lands and earlier times - as with Alexander McCall Smith's Precious Ramotswe in Botswana, or Jason Goodwin's delightful Ottoman eunuch detective, Yashim. The greatest American thriller writer of all, Raymond Chandler, was educated in Britain. Despite Georges Simenon's Maigret novels , the most popular detective novelist in France is Agatha Christie. The only fictional sleuth with instant recognition worldwide is Sherlock Holmes.

The British detective emerged from a particular set of Victorian preoccupations. The criminal investigator, Summerscale writes, was a “secular substitute for a prophet or priest”, a reliable guide in an increasingly confusing, godless and criminal world. The moral implicit in almost all British crime fiction is that intellect will triumph, the crook will be confounded by the rational sleuth, science will track down the malefactors and allow honest English souls to sleep at night. Detectives always have human flaws, for although they are set above us in judgment, they are always one of us.

Allied to this was a darker belief that evil could, and did, flourish in the least likely places. The Road Hill House murder seized the public imagination precisely because the family appeared outwardly reputable, solidly middle class. This suspicion of outward rectitude fed another strand of Victorian fiction - the fear, underscored by Darwin's discoveries, that civilised man was part beast; that behind the veneer of Dr Jekyll lurks Mr Hyde, that Dorian Gray remains young and beautiful while his picture in the attic rots with moral decay.

But if every Victorian might be a criminal, any Victorian might also be a detective. The Road Hill House murder attracted hundreds of letters from the public, offering suggestions as to how it might be solved. The same was true of many notorious Victorian crimes. The letters came from clairvoyants, trouble-makers, gossips and eccentrics, but they were also written by ordinary citizens convinced that what Poirot calls “the little grey cells”, properly applied, could find a moral solution. British amateur sleuthing was and remains an intensely democratic activity.

Those same instincts bubble up whenever a modern mystery erupts: the thousands discussing the McCann case on websites were not acting merely out of morbid curiosity, but exercising the detective instincts that are part of our cultural heritage.

Today the detective genre is more successful than ever. Two rival Hollywood remakes of Sherlock Holmes are in production. The biggest bestseller of all time, The Da Vinci Code, is a detective story.

The twin attitudes that gave rise to the Victorian detective - faith in reason and mistrust of appearances - flourish today as never before. Science, in the form of DNA testing, guides criminal detection more surely than anything Holmes and his magnifying glass could have achieved. But we are even more obsessed than the Victorians with the notion that surface respectability conceals evil. The McCanns were hounded because they might have stepped straight out of the Boden catalogue; Amanda Knox, one of the accused in the Kercher murder, might be the girl next door.

Detective fiction - and its echo in our obsession with real-life murder - reflects the best and the worst in us. At best, a belief that science and reason will triumph, and that inside each of us is a Philip Marlowe, untainted by corruption: “Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid.” At worse, a curtain-twitching voyeurism, an ingrained suspicion that the sweetest smile hides the blackest heart.

As we consume detective fiction in ever greater quantities, we distrust our neighbours and trust in the power of human ingenuity more than ever. Jack Whicher died in obscurity in 1881. We have never needed him more.

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