I’m not quite sure when it was that I began to find the smell of marijuana on London’s streets distinctly irritating. I think it was linked to having kids, as I remember it in parks and playgrounds particularly, conscious that it was only a matter of time before the inevitable “what is that smell, Daddy?” The question eventually came when our eldest was four.

I’m also not sure when this smell became ubiquitous in the part of London where we used to live. It happened so gradually, it went below the radar. In the 90s you would occasionally get the odd waft of a joint as you walked about. When I was teenager, it was rare enough for me to look around out of curiosity, to see who was smoking it.

It was a rude irruption of another world I didn’t want my kids to enter

The frequency of such wafts must have gradually increased, unregistered, until it became a constant background hum: a surreptitious territorialization, so successful that those living within its remit do not even consciously register it.

Then I became a parent. I found it annoying because, when your kids are very young, you’re still in a blissful stage of being able to operate a strict filter over that to which they’re exposed. A smell — permeating the atmosphere and pervading the air we breathe — cannot be filtered. It was a rude irruption of another world I didn’t want my kids to enter.

I’m old enough to remember when “pot smoking” meant crumbling lumps of hash into massive reefers full of tobacco, and a significant number of reefers were required to register an intense high. During the 1990s, skunk gradually took over in much the same surreptitious way that its smell territorialized daily life in certain parts of London. At first, it was exotic and rare, the stuff of legend from older kids who’d got the £50 weekend bus ticket to that fabled paradise of Amsterdam. Within a few years, it was everywhere.

One doesn’t need to belabour the point about the dangers of skunk. Its links to chronic mental illness and violent crime are well-documented. Less well-documented, but still well-known, are the ways regular marijuana use steadily erodes motivation, energy, interest and joie de vivre amongst its users. As put by Geoff Dyer, “Everywhere reeks of marijuana, marijuana that is far too strong and rots people’s brains.”

I saw all this often enough when I was teenager, although there were exceptions. You’d occasionally meet the real enthusiasts — connoisseurs who learned all the finesse of a wine-taster in Bordeaux from their visits to Amsterdam, who could (and always did) ad-lib ad nauseum about chemical compounds, growing techniques and expensive devices, which could then only be bought by mail order from Holland and enabled you to dispense with tobacco altogether. Strangely, the evils of tobacco were often referred to by weed smokers, convinced their leaf of choice was a purely beneficial, medicinal herb.

There was a definite class element to this subculture. The connoisseurs tended to be from the more well-to-do backgrounds: privately educated, well-spoken, with a tell-tale posh English name disguised by a monosyllabic abbreviation that was as unconvincing as their overly-cultivated scruffiness.

Whilst there were sometimes the usual horror stories about psychotic episodes amongst these types, there was never that all-pervasive and permeating sense of an inter-generational erosion of life which I knew from those closer to home, where skunk had become a permanent feature of life for the local community.

Today’s elites tinker with the laws in such a way that they are shielded

That same pervasiveness characterises the takeover of the smell. It went from being occasional to constant, not just because the stuff got stronger smelling and much more intoxicating. The laws governing its usage have been liberalised, and liberalised in a particularly ambiguous way. It was downgraded to the lowest category in 2004, and — although it was put back to its original severity level five years later — in practice it had become something people now accepted as a feature of the urban environment. Nothing much changed, unless the police wanted to make a point.

Last year, the Mayor of London signalled his intention to stop prosecutions altogether — something trialled in three London boroughs, including Lewisham, one of the poorest, where 35 per cent of households have an income 60 per cent per cent below the median level after housing costs.

Around the same time, it was legally sanctioned for medical use. Now someone with a proven clinical need can get a cannabis card (“Cancard”). It doesn’t have a judicial status as such, but it can be used to encourage the police to use their discretion in deciding whether to prosecute someone.

We moved a couple of years ago and left that constant stench behind. I have mixed feelings about it. It’s still a constant feature of life for everyone back home, including the parents and the kids I knew. The fact is that the smell is only a permanent feature of life for people living in deprived areas of the city. Like the posh boys I met who knew all the chemistry and processes, today’s elites tinker with the laws in such a way that they are shielded from being fully exposed to the worst pervasiveness of the detrimental effects themselves.

By making criminal proceedings for personal use of weed dependent on the discretion of the police, certain classes of people are left at the mercy of those things. They were once exotically counter-cultural for discerning adolescent bourgeoisie; now they wreak an inert and stultifying form of havoc on those most vulnerable to them.

Like graffiti, marijuana was once a celebrated conversation point for the younger chattering classes. Now, there are particular subway passages and walls in delimited zones where it is ambiguously “legal” (at the police’s discretion, again). Thus it is kept away from intruding on the built environment of those who buy coffee table books about its development as an underground art-form.

Out here in the suburbs, I still get an occasional waft. I make a point of looking around for the source like I used to twenty or thirty years ago — sometimes I catch sight of a lonely figure sitting on a park bench, looking at his phone whilst puffing away, or a group of teenagers huddled around the ritual I hope my kids won’t be initiated into. More often than not, I think about those for whom even the atmosphere they breathe is stained with the irresponsibility of a legal system that has decided they don’t deserve the benefits of society’s protection.