I’ve been on a book tour recently with the novelist Marcel Theroux, who surprised and delighted me the other day by commenting in our shared dressing room “oh, you smell nice” and then asking “what’s your cologne?”

Let’s leave aside the cultural changes that have occurred over time to allow one man to ask another about what aftershave they might be using and instead think about smell more generally, and how it might specifically relate to crime.

When we detect a smell through our nose impulses are passed along the olfactory nerve to a part of the brain called the olfactory bulb and then processed by other parts of our brain collectively known as the limbic system. The limbic system plays a major role in controlling mood, emotion, behaviour and memory.

Perhaps it’s Marcel’s influence on me, but I am reminded that his namesake Marcel Proust in A Recherche du Temps Perdu (Remembrance of Things Past) suggested that the smells associated with eating a madeleine cake brought back to him memories of his childhood and how his aunt would always give him something to eat before going to church. More prosaically, I know myself that the smell of newly cut hay reminds me of childhood and the farm where I and my sisters grew up.

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The limbic system is often regarded as the “primitive” part of the brain, as the same structure is present in the brains of our distant ape ancestors. Our sense of smell has therefore undoubtedly helped us in evolutionary terms, by allowing us to assess those things which might be good to eat as opposed to those which are poisonous; by alerting us to danger – such as when we smell fire; and being part of the process whereby we choose a mate.

Kissing, for example, is thought by some to have developed through individuals needing to get close so that they could sniff one another and then, well, one thing led to another. Perhaps this is why bad breath remains one of those perennial and universal dating red flags.

Bad breath is bad enough but there are other and perhaps more noxious human smells.

Have you been watching Slow Horses on Apple TV+? Now in its fourth season, this compelling series is based on the Slough House series of novels by Mick Herron, about a bunch of MI5 rejects who have failed in some way but have not yet been sacked.

Their boss is Jackson Lamb, the head of Slough House, brilliantly played in the series by Gary Oldman, who is rude, messy and unkempt. One of his personal idiosyncrasies is that he will fart loudly and publicly, irrespective of whether he is alone, or in company and despite the fact that this uncivilised behaviour serves to mark him as an outsider, as much as it makes him uncouth and ill-mannered.

A scene from Slow HorsesA scene from Slow Horses (Image: free) Lamb’s farting is not used for comic effect, as it was in the 1974 movie Blazing Saddles or, even further back in time by Joseph Pujol who, using the stage name Le Petomane, was a professional entertainer who could control his stomach muscles and fart at will – seemingly to the delight of the audience.

There’s something different going on with Lamb’s passing wind. For example, it serves to distance him from his erstwhile colleagues in MI5 who are supposedly civilised, and who would never dream of behaving as Lamb might and, of course, that distancing means that they don’t get close.

His unkempt appearance and how he smells serve to keep people at arm’s length; they don’t pry; and they certainly don’t want to spend any time in his company. His smell also marks him out as dangerous. It’s here that smell and offending are in my experience linked.

I had to watch recently the bodycam footage of a female police officer entering the flat of a man whose partner had disappeared. The footage showed the officer ringing the man’s doorbell and then being ushered inside. He was chatty, apparently concerned and nothing was going to be too much trouble for him because, of course, he wanted to help to find his partner.

The only problem was the flat was a hoarder’s paradise with rubbish piled high in every room and almost every space seemingly covered by tatty clothes, discarded pizza boxes, old fish and chip wrappers and instinctively you knew that the last thing that anyone would want to do would be to look under that detritus from fear of what you might find there.

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The poor police officer did her best asking question that he seemed only too willing to answer and she left without finding out anything of significance. Weeks later, we’d discover that he had killed his partner and disposed of her remains – not in the flat but at a nearby rubbish dump – and I knew that the hoarding and the associated smells had been a deliberate ploy to keep people who entered his flat at a distance; a means of ensuring that they wanted to get out of there as quickly as possible.

Of course, a dead body in the flat would have created a smell too and over the years I’ve come across offenders who’ve developed numerous and largely unsuccessful ways of masking the smell of their victim’s body that they have, for various reasons, had to keep indoors after a murder.

Thankfully not even an industrial collection of air fresheners is ever going to disguise the sweet, rotting stench of death and it is that putrid smell that is often the beginning of the end for the killer.

Neighbours begin to notice that something is wrong – even more so than normal because, well, he doesn’t look after himself as he should – and pretty soon they are calling the council to fix the drains or, as in the case of Dennis Nilsen’s neighbours, the Dyno-Rod engineer. It was that poor man emerging from the drains, rather than the police who ended Nilsen’s killing cycle.

Oh, and just in case you’re interested, I was wearing Terre by Hermes.

Professor David Wilson is a Scottish emeritus professor of criminology, Herald columnist and TV presenter. A former prison governor, he is well known as a criminologist specialising in serial killers