From racist outbursts on public transport to comedians baiting strikers and disabled people, there's an ugly mood in the air. What's making us increasingly cranky about our fellow citizens? And is there any cure for this modern malaise?

There is a film that is never discussed when people talk about the classics of Hollywood – and with good reason – but nonetheless, The Crazies provides a brief diversion. The 1973 horror flick, directed by George A Romero, is set in anytown USA, a homogenous, god-fearing, God Bless America kind of place. An American version of Midsomer – minus the murders. And the premise is that things go haywire when someone dastardly puts a little something in the water.

Suddenly, strait-laced types start cursing and fighting. Scores are settled. People who want stuff just start taking it. Repressed attractions spring into public view and, as part of that, there's a fleeting, comic glimpse of horny neighbours humping in the high street. A thin veneer disintegrates. What lies beneath?

Britain in December 2011 feels a bit like that place. Nothing to do with the privatised water companies, I'm sure, but for whatever reason, it does feel as if the safety catch has developed a fault, as if the car is on a slope and someone has disengaged the handbrake.

There is an element of devil-may-care to the way we treat each other. You see it on the streets, in supermarkets, on public transport, hear it on the talk shows, read it on the internet threads. Go on to YouTube: three instances now of apparently ratty women berating fellow passengers on the public transport network. Emma West, from Croydon, south London, faces criminal charges for an alleged racially aggravated public order offence. The matter will now be decided by a court. The two others were posted subsequently, with more scenes of acrid cabaret. Women letting rip with barely concealed indecency, broadcasting to all who failed to tune them out that there are just too many foreigners. If that is not enough for you, read the online comments beneath the videos – note the rancourous tone of those who do battle, both for and against. Disregard the contributions from the far right; no one expects decency from them anyway. It is the aggression from those who might see themselves as middle of the road that is worthy of note.

Consider what we say these days to get a laugh. Jeremy Clarkson knows his audience and it is a large, enduring, loyal one that has made him very rich. What would you do to striking nurses? "I'd shoot them," says the jester for our times, and he is unapologetic until the furore threatens his bottom line and forces an apology. Even then, contrition is only partial. People who kill themselves by jumping under trains play havoc with the schedules, complains Clarkson.

Ricky Gervais is even more successful than the Top Gear presenter, a big wheel in Britain and a feted talent in the US. He sees humour in a phrase associated with Down's syndrome. Many object, but still many are with him. We love the comedian Jimmy Carr; it's a big time for him, with DVDs ready for the Christmas market. He also has top stuff about Down's and zingers about wounded British soldiers.

What do we like on the telly? Reality shows, the louder and coarser the better. Shows highlighting celebrities desperate for cash or attention – or both – and therefore willing to debase themselves.

Think about football. The England captain John Terry, ignominious with his fate in the hands of the Crown Prosecution Service amid disputed claims that he called Anton Ferdinand of Queens Park Rangers a "black cunt". Football, always a pressure cooker, continually reveals much of what lies beneath. While the judicial authorities ponder Terry's case, the Premier League wonders what to do about Luis Suárez of Liverpool, who may or may not have racially abused Patrice Evra of Manchester United during a high-profile fixture. This despite all the efforts over several years of campaigns such as the anti-racist Kick It Out initiative. The big boys lead by example. Muslim players with beards who turn out in the lower leagues go prepared each week for the likelihood that someone will try to provoke them by calling them "Bin Laden".

Think about schools, where an ebullient, engaging New Zealand-born teacher called Suran Dickson has felt moved to leave her job and launch a charity to try to curb the worrying incidence of homophobic bullying in our schools, where terms such as "gay boy" and "homo" are playground missiles of choice. Where do these attitudes come from, I asked her the other day. Mostly their parents, she said.

If someone hasn't taken the handbrake off – facilitating a slow but steady decline towards grouchiness and intolerance and not a little meanness – it certainly feels like it.

How did we get here? There are many theories from which to take your pick. An obvious one is money. For the past decade we had a lot. Or at least, with plastic prevalent, it felt as if we had an unlimited supply. Now we know better, and we don't like it. The prime minister says we are all in this together, but no one believes him. The immediate landscape looks rocky for most people, and, beyond it, the going looks increasingly impassable. Wages cut, jobs lost, services run down, disillusionment with the establishment and the political class; little wonder people are cross. And, as we know, angry people behave badly.

Cary Cooper, professor of organisational psychology and health and pro vice chancellor at Lancaster University, says we are witnessing "an exercise in civic frustration" – hard times cause fear and insecurity. "People feel financial insecurity, job insecurity," he says. "They don't even trust the health service. They feel social insecurity and project it on to other people. They can't get angry at the government or the bankers or economists or the NHS, so they take it out on others they can get to."

He is surprised to one extent, he says. "I am an American and I have lived here for 30 years but I don't quite understand what is happening. In the US, they blame a lot when things go wrong and go over the top when things go right – so you have Steve Jobs, for example, as a hero for our lifetime. Here one expects something different. What is happening is the opposite of the 'Dunkirk spirit'. There is a lot of blame culture and I think it is rather sad. It's cathartic for people personally, but it doesn't solve the problem; in fact, it makes things worse by creating negativity. Maybe if things do actually get worse, that Dunkirk spirit will kick in."

But there is something else that has less to do with money and more to do with politics. That cannot be blamed on the vagaries of the financial system or voracious brokers selling mortgages to people who cannot afford them. This was not foisted upon us; this was a choice. Two years ago, amid the deafening clamour of complaints about the scourge of "political correctness" – wails and lamentations from a crew diverse enough to include David Cameron, PD James and Cliff Richard – I wrote a piece for the Guardian site Comment is Free pointing out that those who complained of being silenced by political correctness were usually the ones who enjoyed a platform to make politically incorrect pronouncements, much like errant schoolboys hurling stink bombs into public places. I posed the question: "What would they be like without a handbrake?"

The thesis bears repeating. "Political correctness has become the complaint of choice for those who don't like their world; for men who fear their positions are being eroded by women, white people who fear too much attention is being paid to non-white people, minorities jealous of other minorities, non-disabled folk who can't see why buses should have wheelchair ramps, tall people who fear short people. It embraces everything. It means nothing."

Which was true, but that did not mean it was without value. As a concept to be built up by the right and then knocked down, "political correctness" was pretty useful. It gave a disparate battalion of the aggrieved something to rally round. They fought the fight, and any honest evaluation would have to conclude that they have been pretty successful. Anything that smacks of being PC – including moves against racism, sexism, gender discrimination or homophobia – risks being confronted by the right as just another example of the old discredited orthodoxy.

There was a battle of ideas. And, the war itself is not over. But for now, they have won. And the result is a country that is a bit less civil, a bit more selfish, a bit more reckless over the sensitivities of others. This was inevitable. Those who argued against the boundaries they perceived as part and parcel of political correctness and railed against equalities cannot credibly complain about the scratchiness and volatility of life with the handbrake off. They fought long and hard to disengage it. People such as the honourable member for Shipley, Philip Davies, parliamentary mouthpiece for the Campaign Against Political Correctness, who has been seeking to tie up the Equalities Commission with inane questions, the better to make his political point. His puzzlers include: "The Black Police Association. Isn't that racist?"; "Is it OK to black up one's face?"; "Is it racist for a policeman to refer to a BMW as 'black man's wheels'?"

Let's have a shout out for the Tory MP Matthew Hancock, who apologised for the last government's Equalities Act to businessmen at a fringe debate at last year's Conservative party conference – the act was aimed at outlawing discrimination in the workplace. You can rely on us to undermine it, he said. And then there is Peter Davies, father of Philip. He was elected in Doncaster for the English Democrats, pledging to sweep away all vestiges of political correctness. He discovered on the morning after his election that much of what he had promised to do was probably illegal.

All did their bit. For all that, life without the social handbrake and the decency so often denounced as political correctness does not seem to have made them any happier. No one has benefited from it, really.

Linda Bellos, chair of the Institute of Equalities and Diversity Practitioners, says the problem is not a large group of people, but an atmosphere created by a small group of people, which has an impact upon everybody. "They have made it OK. There has been a period in our recent social history in which it was not acceptable to say certain things, but now people feel they have the authority," she says. "We are entitled to think what we like about each other. We have freedom to think. But morally, we do not have unfettered freedom of expression. There are things we can say but don't. People think it is OK to speak ignorance and hatred. They think they have the green light."

The authority, claims Bellos, comes from the top. "If you look at much of the rhetoric about taking back powers from Europe, for example, much of the legislation being described refers to equalities. When ministers speak about it, they are using a kind of code."

We are free societies, with freedom of speech and the right to offend, but all civilised societies need some kind of handbrake. The alternative is Lord of the Flies spanning several continents. Our main brake is the law and the judicial system, but before things reach that stage there is just us, making hundreds of micro-decisions each day about how we view and treat our fellow citizens.

Perhaps, as Cooper suggests, there is a cultural element here. Some societies are known to be faster and louder and brasher and less forgiving than others, as many people find when first they arrive in London, and any Londoner discovers when making the adjustment to life in Manhattan. There is a spectrum embracing, at one end, those countries where the general culture seems relatively gentle and, at the other, those that require a strong nerve and a flak jacket. We had a particular place on the spectrum. One senses that we have moved.

What to do? Well, the first thing to understand is that the handbrake that has been disengaged can be reapplied. There is a sense of right and wrong within the British psyche. The ratty YouTube women may have held centre stage, but it is worth noting that, in each case, their outbursts were challenged. Some may have agreed with the view that the country is overrun with migrants, but one could do that and still feel outrage at the way these people chose to behave.

We bait celebrities and other masochists who volunteer for televised humiliation, but at some point there is always a public row about degradation. We err, we stray, but we know we have a default position and we retain a rough idea of where it is. John Terry holds a high-profile role representing his country, but when the allegations surfaced, he found himself the subject of police inquiries and a candidate for prosecution. One wonders if the captain of a national team would have endured such public criticism for a sin of alleged racism if that nation were Italy or Spain.

And that is a point worth ending on. For even if things do seem to be unravelling a bit, this is a still a small island nation that strives, with some success, to fuse the destinies of people who have been here for hundreds of years with those of people who arrived yesterday. People with all sorts of complexions, all kinds of lifestyles; people with strong religious beliefs, people with none. We live together in cities, not in silos. We tend not to pry, but, if needed, we try to help. We try to live and let live. There are problems – the events of a turbulent summer and all we learned from those who were involved show that. There are serious challenges. But given the potential for division and societal dysfunction, the record is pretty good. It is right to take stock, and hopefully we will return to equilibrium, emerging a little less cranky. Still, the UK with the handbrake off remains a better place to be than many others with the handbrake firmly engaged.