IT is as well for the future of the nation that our politicians, without exception, enjoy a peculiar genetic advantage over the rest of us. Try as they might, not one of them - not a single one - is ever capable of enjoying cannabis. Back in the funky, distant days of youth - never last week, for some reason - they "experimented". Alas, "it did nothing" for them; "it had no effect"; and the smoke, presumably, got in their eyes. Remarkable.

Home secretary Jacqui Smith, and several fellow cabinet members, have joined the ranks of the confessing non-sinners, the Clintonite breathing-not-inhaling elite. In some political circles the admission is now almost a rite of passage, proof that you may know, roughly, what you're talking about when dope is mentioned. Since Smith is about to reclassify the drug from "not very" to "somewhat" dangerous, her own revelation is well-timed. But let's not call this a career high, as it were.

She attempted cannabis "just a few times" - well, you have to be sure, don't you? - at Oxford University in the 1980s. Of course, being a future politician possessed of special DNA, she "did not particularly" enjoy it. She is not proud of her younger self now. "I did break the law I was wrong drugs are wrong," she told the BBC.

Drugs are wrong? Surely drugs are either dangerous or not dangerous. Chemicals have no moral standing and addicts, where they exist, have physical and psychological problems. They are not ingesting an ethical defect. Their status as criminals, much like the renegade student Jacqui Smith, depends on home secretaries who dither over whether cannabis is no worse than a prescription antibiotic ("Class C") or something that merits imprisonment ("Class B"). Does Smith believe that drug-users are bad people?

Presumably she refers only to the degenerates who actually enjoy the stuff. You can imagine the Home Office briefing. "But why are so many teenagers doing this?" "Well, minister, according to our very best research, it turns out that the young reprobates like it."

In order to be in a position to lecture the rest of us, politicians cannot admit to guilty pleasures. Smith claimed last week that her confession proved that she is "a human being". I hadn't heard anyone suggest otherwise, though with New Labour you can never tell. By her own account, Smith is just like us, but with the crucial political difference that she is incapable of actually enjoying our filthy habits, and therefore free to moralise. And legislate.

Backing up his boss, Home Office minister Tony McNulty also admitted that he, too, had flirted with reefer madness while a student. If anything, he went one better than Smith, having merely "encountered" cannabis at university. Which is to say he had a close encounter by smoking it "once or twice". This was the variant of the standard line proffered last year by Vernon Coaker, also of the Home Office - what is it with that ministry? - who said: "When I was a student, I took one or two puffs of marijuana, but that was it".

At least eight Tories and a bunch of other Labour people have made similar disclosures. The line is always the same: couple of puffs, didn't care for it, saw the error of my ways. Is it just me, but wouldn't this fad for drug-related reminiscence be just a tiny bit more plausible if one of them, just one, said: "Yeah, sure, I was the biggest dopehead in the college. Out of it morning, noon and night. Didn't turn me into a psychopath, of course. Are you looking at me, by the way?"

It seems bizarre, nevertheless, to hear upholders of the law admit to past crimes while denying the sole motive for illegal recreational behaviour: you do it because you like it. It seems odder still - or do I mean merely hilarious? - that these people should then pretend to have special insights thanks to their wholly unproductive "encounters" with a substance. It is like nothing so much as the person who loathes the very taste of whisky claiming to understand alcoholism. And about as believable.

Just before you skin up - no crumbs on the picture byline, please - bear this in your short-term memory, though. Cannabis, in certain of its modern forms, gives some pause for thought. Even five years ago I would have dismissed the idea that it counted as any sort of health hazard in a world of smack and superlagers. Yet some of the newer, home-produced dope offerings, their active component (delta-9-tetrahydrocannabinol, if you care) amped up, are beginning to produce reports of casualties.

The research is not clear, as ever. Do skunk and the like induce mental illness, or is inevitable mental illness in the susceptible merely hastened by a drug that has become too hard to handle? Politicians such as Smith, supported by some doctors, are inclining to the former. Prime minister Gordon Brown has therefore called for the classification of cannabis to be reviewed by the Advisory Council on the Misuse of Drugs, via the Home Office. Hence, one suspects, the home secretary's "confession".

Whether another reclassification in three years would make a blind bit of difference is open to question, I would say. Recall, also, that only last year the advisory council reported on this very subject. It found that there is certainly scientific evidence to suggest a link between cannabis use (how much use?) and "long-term psychotic symptoms", but concluded that the risks are not serious enough to warrant a Class B rating.

The work has already been done; the dangers assessed. Yet Brown (never, ever touched the stuff, says Downing Street) and No-Buzz Smith want the issue revived. How many wars on drugs can one country stand? How many politicians with a remarkable immunity to narcotics do we still need? Or would a small moral panic speed the social policies of the new Brown government on their way? Tough on illicit pleasures; tough on the chemical causes of illicit pleasures. The alcohol industry must be dreading the next, logical step. Right.

At this point, we could rehearse all the arguments for and against prohibition. We could wonder over the risks of passive smoking at Edinburgh University when the new prime minister was a student there. We could kick around old arguments over the status of dope as a gateway drug, or pause to wonder what's become of the young folks nowadays, eh? I still struggle to get beyond the procession of politicians who find it useful, suddenly, to admit to their involvement in past non-events.

It says something about the relationship between the governing and the governed. If Smith had told us, last week, that she once smoked a bit of dope, like many students, and that like a lot of them she enjoyed it for a while, the contribution would have been useful. She could have added that no real harm was done, that she soon put the tiny vice behind her and then got on with her studies. Don't smoke dope, kids, she might have said, join New Labour instead. It's mind-altering.

Instead, Smith had to tell every news channel available that she was "not proud" of her crime, that her drug use was "wrong", and that she was still a human being, despite it all. You might think she had spent her student years biting the heads from budgies. You might think, more to the point, that she has forgotten the realities of the country in which she lives. As a matter of information, it is not a country in which many thinking people are addicted to guff.

An awful lot of them refuse to believe that cannabis is so very bad. Millions use it daily, apparently. Reports of increased numbers harmed may simply reflect, as a fraction of those already unstable, wider use. We don't really know. But politicians with a magical physical indifference to a drug are perhaps not best placed to enlighten us. They still claim always to know the difference between wicked and virtuous, however, and that's just silly.

Still, it keeps them in a job. And off the streets. And off the dope to which they, once upon a time, just said no. That must be why they know what's good for the rest of us even when, as they continue to insist, they don't actually know what they're talking about.

Someone must be on something. I don't think it's me.