By their Wranglers you shall know them. And by their lines of coke after Sunday lunch. The baby boomers, a socio-economic group so strong they have their own version of Trivial Pursuit, have been reassessed and found wanting.

A piece in Time magazine this month — “Balding, wrinkled and stoned” — assesses the national cost to America of boomers engaging in what it calls “a 40-year high”. According to data presented by a National Institute on Drug Abuse conference, the United States is bracing itself for a significant increase in the number of older adults suffering from “substance use problems”.

At the same time a new book, Boomergeddon, by Mike Males, a California-based academic, says that the popular view of the boomers — born between 1945 and 1963 — as the happy, prosperous product of the post-war economic boom, is off the mark.

The boomers, he says, have carried their wayward, irresponsible ways into adulthood. In California they present the state’s fastest growing age group for petty felony and the biggest demographic for HIV/Aids. But most damaging is some boomers’ casual enthusiasm for drugs. Today’s California drug addict is more likely to be 45 than 20. “No one wants to hear it,” says Males, “but we’ve got a problem with the middle-aged.”

In Britain we have a similar story. Our post-war baby boom accounts for 20m people, or about 40% of the population. And although plenty now have a paunch hanging over the waistline of their Wranglers, many continue to act as if they were still in that glittering moment poised between the Chatterley ban and the Beatles’ first LP.

“There is a dental surgeon I work with who is 51, exactly my age in fact, who allows his teenage sons to smoke dope at home,” says Jill, a London GP. “He isn’t worried at all, because it’s what he did and still does. He thinks it’s about the same as having a drink. I think it’s part of his lifestyle.”

“When I first joined the BBC,” says Georgina, a light entertainment director, “older people would try to get their work done by lunch. They all thought they were so clever. We, the young ones, worked all day because we were terrified of messing up, but their behaviour went like this. Finish work by 12.30. Go to a posh restaurant, get really pissed. By about nine or 10 in the evening it would be time for the drugs to come out.”

Another BBC staffer concurs. “It’s joints at each other’s houses and coke when out and about,” he says. “This lot grew up with utter confidence and job security. Of course, it’s not until now, in their fifties, that they are at risk of f****** up at work. It affects their families: I knew a bloke who took coke with his dad and his girlfriend couldn’t handle it. She had to end the relationship.”

Keith Allen, the comic actor (born 1953), says: “I think the reason is that we were the first generation to have a reason not to follow in our fathers’ footsteps. Nowadays a lot of kids see their dads going to buy their crack pipe. There is nothing to rail against if your father is on the same drugs as you. We will be the first generation to take our record collection to the grave with us. And the Arctic Monkeys are as much for us as they are for 18-year-olds.”

“I call it the ‘Saffy factor’,” says James Runcie, the writer (born 1959). “You have daughters who disapprove of you. They think you are just a bit pathetic, stealing their youth. Parents taking drugs is worse in their view than parents having sex. Our daughter Charlotte hates it that I have got the Killers on my iPod and bought the Arctic Monkeys before she did.”

Drugs are just a part of everyday life to the boomers, says Chris Jeans, the documentary maker (born 1945). “They think of them as things to take to make things better, to help you get out of misery, depression or whatever. One of the successes of the 1960s is that it reshaped the way life is lived and a lot of old-fashioned moral attitudes changed as a result. It’s not that we were degenerate, but our attitudes changed the way society looks at things, from homosexuality to feminism.”

One of the most marked characteristics of the boomers is their refusal to grow up: the continuation of a life lived as if they were still in their twenties. “Why do we still go to Glastonbury and not sit around knitting for our grandchildren? We formed a new paradigm, a lifestyle motivated around music and fashion and community,” says Lynne Franks, the PR guru (born 1948). “I think it was LSD. Not that I personally used it, but it had a huge effect on us and on our philosophy.”

Although she is very positive about her children and her grandchildren, she fervently believes that it is her generation which had the experiences that count. “People used to think that at 50 they should be getting ready for old age,” she says, “whereas we baby boomers are getting ready for life. Forget the gap year. This is my gap life.”