John Walsh: 'If you walked through the back quad you'd soon be as stoned as a poodle'

Tales of the City

What was William Hague up to, when he told a Sunday newspaper that MPs should confess about their youthful drug experiences? The shadow Foreign Secretary showed no inclination to spill les haricots about his own youthful drugs regimen, but he seemed oddly keen that others should. "There are many leaders of countries who have been into some kind of drugs," he said, mystifyingly. "I think openness is 90 per cent of the answer with anything you've done wrong."

Was he trying to embarrass his boss, Mr Cameron, who always shies away from questions about drug use, saying only that he had "a typical student experience"? Or was he saying that, if many ex-stoners are now perfectly fit and able to lead their countries without gibbering with paranoia, maybe drugs aren't that bad after all?

A curious position for a senior Conservative to take. And how unwelcome his views will be to the people at Frank, the information service run by the Home Office and the Department for Children, Families and Schools, which has just launched a £2.2m TV campaign to warn teenagers that "the more you mess with cannabis, the more it can mess with your mind". It will be on your TV screens soon, giving your 11- to 18-year-olds the willies. It shows a student squat inside a human brain. The occupant, a gormless youth in a zip-fronted fleece, smokes a joint and answers the door to a succession of clones of himself: they start out harmless, labelled "Giggles" and "Talkative", but later become "Pukey" and "Panic Attack" and worse.

When you've blown two million quid on this message, it's unhelpful of Hague to say (or at least imply) that drugs didn't do world leaders any harm – as if the chap in the TV commercial, after puking and suffering panic attacks, might end up labelled "Future Prime Minister" and "Latter Day Global Statesman". How annoying for the Home Secretary, Jacqui Smith, who admitted last year that she smoked cannabis when young. How annoying that she's not a picturesquely traumatised wreck as a result of her flirtation with narcotics.

There's a large, personal question here, however. Not whether MPs should come clean, but how fiftysomething parents should tell their children about their drug-use. My younger children are now 17 and 13, right in the cross hairs of the new drug warning. But how should I advise them about something I enjoyed at university?

Baby-boomers have a tendency to brag about their wicked pasts. In the mid-1970s, everybody smoked dope: on Sunday afternoons, if you walked through the back quad of my Oxford college, and there were enough windows open, you'd be as stoned as a poodle by the time you reached the lobby. Some of my fondest memories are of BFJ (Big Fat Joint) Nights on Fridays, when my housemates and I stayed in, smoking, playing records and giggling at tiny things (some lyric or word or noise) that struck us as hilarious and that we repeated with manic glee. We weren't being cool. We were being terribly silly, like children.

That was how I represented cannabis to my eldest child. "It just makes you act very stupid. If that's what you fancy, OK, but you could do something more interesting with your time." Then, at a literary festival, I met a bohemian cove called Marcus, whose charming son George was a chronic dope-smoker in his twenties. It didn't seem to affect his ability as a graphic designer, and Marcus wasn't unduly worried. "George gets fixated on odd things," he said, "but then he's OK."

A year later, it wasn't OK. George twice tried to kill himself – and finally succeeded, under the wheels of a lorry on a Gloucestershire road. What had happened? "He couldn't stand this thing in his head," Marcus told me. What thing? "Some phrase or random words, or some tune," said Marcus. "I couldn't make him tell me. It just pinged away in his head, over and over every day like a stuck record, and drove all his other thoughts away, until he couldn't stand it."

I'm not going to speculate whether George's fate was all the fault of modern-day skunk, and that "ordinary" cannabis is really good for you. I just think about my friends and our hilarious Friday nights in 1975, and how damned lucky we were not to get a shard of repetitive madness lodged in our brains for ever.