So we’re sitting on a shaded cafe terrace enjoying a leisurely aperitif as the sun sets over the Mediterranean. A mobile chirrups - text incoming - and one of the company of middle-class, middle-aged Brits scans her message. It’s from the teenage daughters who have been left at home in Bristol for the weekend.

“They’re after our dealer’s number – they’re planning a chilled night in and want something to smoke,” explains the mother, who runs her own interior design agency, and texts back. Later, a fresh message confirms that the enterprising merchant has turned up on his bike and sold them some cannabis. Sorted.

From the distinguished lexicographer who told me how he and his 14-year-old son regularly “skin up” together (a rather masculine, clubby activity, apparently) to the chaotic family life of permanently twatted council estate patriarch Frank Gallagher in television’s Shameless, intergenerational dope smoking seems to be more common than sit-down family meals these days. The kids of the 1960s and 1970s are handing on the toking habit they haven’t quite managed to shake.

Last week Nicola Cooper, a 43-year-old Suffolk primary school support assistant, was sentenced to 200 hours’ community work for giving cannabis to her teenage son and daughter. Cooper, who said she had been an occasional cannabis smoker since the age of 18, became her children’s supplier because she and her husband Ian Leppard, a 51-year-old company director, didn’t want them to get involved with dealers who might tempt them onto harder drugs.

Enlightened liberal parenting – or a dangerous dereliction of duty? Cannabis is increasingly believed to be a trigger for mental illness, especially in the young. And it is illegal – a conviction could seriously scupper career and travel prospects. The maximum penalty for possession is two years in prison and a fine. The penalty for supplying can be up to 14 years – and theoretically this could cover simply passing someone a joint.

Cooper escaped the full might of the law in Bury St Edmunds last week because district judge David Cooper said “she has an excellent character” though he added that he thought she was “utterly misguided”.

Dr Pat Spungin, psychologist and founder of the advice website www.raisingkids.co.uk, thinks Cooper was undermining her children with mixed messages. “She was saying, ‘Get it from me because I won’t tempt you to anything stronger’, but she was also saying, ‘I trust you so far but no further. There are people in the world I wouldn’t want you to associate with, but the drug is okay’.

“Are her children sufficiently inculcated with the values to know when and where to stop? She obviously doesn’t think so.

“Parents stand for the adult world, society and the law beyond and behind you. Freud was right, the parent is always the super-ego, embodying the conscience, values and morality of society.”

But what about reflecting a society where respectable mums like Cooper smoke dope as “a relaxing thing”?

The default teenage setting of bemused contempt for their parents’ chosen lifestyle does not always result in an AbFab Saffy-style reaction to a laid-back relationship with narcotics. The holiday acquaintance who kindly passed the dealer’s number on to her girls recounted how, as the liberal dope-smoking parents, their house becomes the weekend destination of “a herd of gazelle-like teenagers who come down from my girls’ bedrooms to drift blank-eyed around the house, leaving a trail of total devastation in the kitchen or giggling inanely at Sponge-Bob SquarePants on the TV. They get in the way, they make an appalling mess and we’re fed up with them”.

But as the only parents at their daughters’ exclusive girls’ school who tolerate such behaviour, they’re stuck with it, and accept it as the price of a family policy of openness and honesty. Not total frankness, though – in the interests of keeping on the right side of the kids, she does bite her tongue about wishing they’d all just push off. But she’s more honest, she reckons, than parents who have either never inhaled, or conveniently forgotten their youthful excesses, and are unwilling to accept that drugs will come along to tempt their children, however careful their upbringing or expensive their schooling.

Yet she might also be dangerously out of date. Sarah Graham, a recovering addict, addiction therapist and spokesman for Frank, the government-sponsored drugs information service, warns: “I would encourage parents, even those with a history of smoking themselves, to get up-to-date information.

“They might have an established route of supply but out there cannabis has changed. Skunk – the stronger herbal strains of cannabis – is now a brand in itself. That’s what young people are interested in.

“And we do know that cannabis use, as alcohol use, can have a long-lasting impact on teenage brains. As a therapist and person in recovery I’ve treated young people with cannabis psychosis – a really distressing condition.” Which might make even the most laid-back parent start to question the wisdom of tolerating, let alone condoning, their child’s introduction to such a substance.

However, Frank does not go so far as to recommend a good old-fashioned parental ban.

“If I was a parent, I wouldn’t encourage my young person to smoke cannabis but to get the facts before they start smoking,” is as prescriptive as Graham will get.

But the Cooper case has got her thinking. “My dad took the liberal route and allowed me to spliff up in my bedroom. At the time I loved it – how cool! I took magic mushrooms with him. In his defence, I was a nightmare teen after my mum left – but even so, I wish that the boundaries had been a little firmer.”

A friend who manages a small record company with a young staff has no illusions about the ubiquity of drugs in today’s society. She wearily describes the way last year’s office Christmas drinks descended into a drawn-out cocaine splurge when all she wanted to do was get to Waitrose before the organic turkeys sold out. She doesn’t enjoy drugs herself, but started talking to her children, now 16 and 14, about them when they were still in primary school. “I didn’t say don’t do it. I just told them what might happen and how to deal with it if you get worried or scared,” she says.

“What I’ve always said is one day if it happens be with people you know and trust and don’t be frightened to ask for help – come home and say I’ve done this thing and I don’t know what to do. The worst thing would be for a child to be too scared to ask for help from their mum and dad.”

Spungin agrees: “Children need a responsible adult to talk to when they need to. I’ve known parents who have been very hippyish and tolerant – till one day their child’s tutor said to them, ‘She’s very dopey in class sometimes’ – at which point they realised with a shock that their laissez-faire attitude was actually damaging her education.”

Cooper has learnt her lesson about cannabis. “I don’t want to touch it again,” she said last week. Perhaps it’s time the rest of the nation’s dopey parents grew up.

Some names have been changed

Read more on this at our alpahamummy blog

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