Last week's air-rage incident was another example of a trend towards gross behaviour in public. What's gone wrong?
The hefty lad in the Dallas Cowboys anorak sat on the opposite side of the train carriage, head in hands, spitting on to the floor. A friend ranted into his ear, spattering the air with four-letter words. The puddle of white, foamy spittle grew until it touched my shoe.

It was disgusting. The combination of powerful profanity and careless, sprawling body language was threatening. But it was nothing really, the sort of low-level territorial violence that anyone who travels on public transport has to get used to.

Better make that anyone who goes out in public because, as you know, as your parents knew, and their parents before them, things ain't what they used to be. Successive generations always moan that standards of public decency have fallen since their day, but is it true? Is Britain behaving more badly than ever?

It doesn't take much for even the most right-on, live-and-let-live people to start saying so. Last week's catalysts for complaint were the Virginia 12, those travellers stranded on the wrong side of the Atlantic following an incident in mid-air.

They claimed to have been indulging in nothing more threatening than a good old Irish sing-song, but the Airtours flight crew were sufficiently worried to ask for an emergency detour. So instead of sunning themselves in Montego Bay, the caravan-dwellers of Lewisham found themselves camping in an American airport lounge with only the world's press for company.

AIR RAGE was sweeping the skies, said the International Federation of Air Line Pilots' Associations. Incidents had almost quadrupled in the last three years. There were tales of other Britons punching out aeroplane windows, indecently assaulting cabin staff or threatening to kill the captain.

Bad behaviour was hardly confined to the clouds, however. A court heard about the West Country wedding to which the riot police turned up as uninvited guests. Four armoured vans were called out to deal with a brawl between at least 70 of the 100 people at Donna and Shane McLaughlin's reception in Bristol last August. CS gas was used to break it up.

Anecdotes and crazy stories do not constitute proof, but a review of the evidence last year was clear in its findings: "Overall crime rates, including crime by juveniles, have risen greatly over the last half century, and this has been paralleled by increases in many psychosocial disorders among young people."

The report, Antisocial Behaviour by Young People, was compiled by authorities in child psychiatry, criminology and social psychology. While pointing out that much antisocial behaviour went unreported, they said it was obvious that crime committed by young people had become more violent. Most of the perpetrators were male, as ever, but young women were increasingly involved. Trouble-makers like football hooligans, lager louts and those who rage in the air or on the road tend to be adult, but the report argued that antisocial behaviour was learned in childhood.

A number of environmental influences must share the blame, it said. Family breakdown had increased, causing conflict and disruption. Adolescence had become even more confusing, as teenagers were expected to be more independent but spent longer in education.

Drug and alcohol abuse had increased, as had the opportunities for crime. Altered shopping and housing patterns meant there were more things to steal and it was easier to go about life unwatched. Public attitudes to what was acceptable had also changed, partly under the influence of the media.

Alison, who teaches eight-year-olds in east London, agrees that attitudes have changed since her schooldays 20 years ago. "Children answer back in a way that no one of our generation would ever have dared. It's not just teachers, it's a general erosion of respect for authority. You start with nothing and you have to earn their respect.

"By year six they're really big for their boots. There are instances of knives and air pistols being found in junior classes, and children throwing chairs around. There is far more of that than there used to be."

As a child of the Sixties, she grew up believing that a certain amount of distrust of authority and questioning of conventional wisdom was a healthy thing. "The trouble is we've overshot the mark and gone completely the other way."

It used to be easier to know what the problem was, and how to fix it. Those on the right could argue that all you needed to learn discipline was a damn good smack or a spell in the Army, while the left blamed poverty and deprivation. As usual, New Labour has muddied the political waters, by pledging both to spend millions of pounds on run-down estates and to crack down hard on crime.

Restraining orders are to be placed on persistent small-time troublemakers, as the Government pursues a social policy inspired by the fashionable American theory of zero tolerance. This says that wiping out the pettiest of crimes creates a climate in which the number of major offences also declines.

They believe something similar at London Underground, where new poster campaigns will be launched in May encouraging passengers not to put their feet on the seats or play personal stereos too loud. "We do try to discourage antisocial behaviour," says a spokeswoman. There have been notices on trains exhorting passengers to better behaviour "since God was a boy", she says, although new ones have been developed in the last few years in response to customer complaints. "People do seem to be less considerate of others now than they used to be, in general."

The night the Dallas Cowboy spat on my shoe I noticed a sign asking passengers not to eat smelly food in the carriage. A poster on the platform showed a blurred picture of an escalator above the words: "Take extra care if you've been drinking."

Kate Fox, director of the Social Issues Research Centre, is not impressed. "Once you start banning things and littering the place with authoritarian, officious notices, you draw attention to this behaviour," she said. "This idea that people have to be told how to live their lives is wrong and does not work."

She does not believe that things are getting worse. "There has always been, and always will be, antisocial behaviour. It is part of human nature. Greek and Roman literature is full of people bemoaning the behaviour of the younger generation.

"When you give a name to something people imagine it is a new phenomenon, or on the increase. Road rage is nothing new. There are examples of it in Jane Austen, involving horses and carriages. There is a serious boy racer in Northanger Abbey."