Last week, Maureen Lipman admitted that in the 1960s she took LSD and cannabis. Well, would you believe it? Maureen Lipman! The 1960s! Taking drugs! An actress taking drugs in the 1960s! I've never heard of such a thing! What's the next headline-grabbing revelation going to be? David Tennant wore flares as a child? John Sergeant once threw up during his student days? Keith Chegwin took two bottles into the shower?

Lipman's admission (to be broadcast in a documentary series starting tomorrow night on Five) may have created a new unit of measurement - a Maureen - for the smallest, most unremarkable piece of news it is possible to record: it's about a tenth of a celebrity divorce or half a failed traffic-calming measure. Lipman's is just another tiny voice in a titanic chorus of prominent people saying that they dabbled with drugs, didn't really like it and moved on. Couldn't we just assume that they'd all had a go unless they specified otherwise?

After all, in 2000, when loads of the shadow cabinet were coming out as having smoked cannabis, the only thing I found memorable was Ann Widdecombe saying she hadn't. The nation's dealers must have been rubbing their hands: Ann Widdecombe, the face that launched a thousand shipments. If she cared about our nation's youth, she'd have kept quiet.

But the fact that everyone from Helen Mirren to Francis Maude has had a druggy phase presents a problem for anti-drugs campaigns - because most of these people are clearly fine. They didn't go through 'drugs hell' and they didn't die. They had a go, it didn't take for whatever reason and then they went off and were successful. 'By all means, try it but you probably won't like it' isn't quite the message that government agencies want to put out. Unfortunately, those who tried it, loved it and were destroyed by it don't seem to get interviewed on chat shows very often.

Time for my own drugs admission: part one, I smoked cannabis a few times at university. I treasure the idea that anyone is scandalised by that. They've got a life-full of shocks coming if they are, because I am a very timorous, conventional, largely law-abiding man and, if I've smoked marijuana, then almost everyone else of my generation must have done if they've got a mouth.

That's certainly a bad thing - we'd all be either better or no worse off if we hadn't - but if anyone's still lumping pot-smoking in with dirty needles then they're living in an episode of Quincy. It's more something a married couple of solicitors might do in their garden (not indoors - it makes the curtains smell) while they discuss moving to be near a good school. (Public Service Announcement: I'm talking about normal cannabis here rather than skunk which, I'm reliably informed, both is, and can get you into, serious shit.)

Part two of my drugs admission is even more shaming: I have never been offered cocaine. And that's not just hurtful, it's annoying. I long ago decided, you see, that I would refuse. I already drink too much, so why would I risk adopting another harmful habit? If I tried cocaine, the worst outcome would be that I liked it and the best that I didn't. When not liking something is the most you can hope for from consuming it, that's a good reason to abstain.

Do you like my logic? I was pleased with it and looked forward to delivering it to the twat I imagined offering me a 'line' (I lack the confidence to type that without inverted commas) at a party. But not once have I been given the chance! Clearly, I come across as too square even to be worth attempting to corrupt. I'm just not cool.

'Cool' is the key to all this. That's why the celebs are happy to make their admissions. They're boasting that they were the kind of people who were cool enough to be approached, to get involved, to try stuff. They were creative and experimental and dangerously unwise and there's no one alive who, at some point, didn't want to seem like that. Except maybe Ann Widdecombe.

This is also the problem with anti-smoking campaigns. They persist in trying to persuade kids that smoking isn't cool. Come off it. Look at Sean Connery as James Bond or Béatrice Dalle in Betty Blue. We're trying to stop millions of young people from doing something that may kill them and we kick off with a demonstrable lie.

Smoking is cool. Addiction isn't (people huddling outside offices in the rain don't look cool so much as cold) and cancer certainly isn't, but smoking when isolated from these things obviously is. No, there's a harder but ultimately more persuasive message we need to find some way to convey: being cool doesn't really matter. We shouldn't let 'cool' become a direct synonym of 'good'.

The problem is that to the marketing and advertising companies this is heresy. Invoking 'cool' is how you make people do things they otherwise wouldn't: buy electric shavers that jizz moisturiser, endlessly drink mini-yogurts, douse themselves in a smell Kate Moss has reportedly made. Cool is why they're smoking, so it must be why they'll stop.

We'll never stop the young from wanting to be cool and it's worth promoting uncarcinogenic ways they can do this. But we might as well spend some time trying to undermine being cool as an aim, rather than pretending we know better than them what constitutes it.

It irritates me when teenagers in bad dramas or adverts say things such as: 'Your mum's cool' to mean: 'I like your mum.' The correct response should be: 'No, my mum is not cool - she doesn't wear sunglasses indoors or weird clothes. She is a middle-aged woman who is nice and good and wise and worrying about what's cool is beneath her.'

Unfortunately the reply to this would inevitably be: 'Cool!'