Many in the UK are reeling after days of images of brazen thefts and wanton damage during the riots, but just where is the tipping point when people think they can start looting?

There have been some extraordinary scenes in London and other cities this week, from burning buildings and running street battles, to people unashamedly walking into a shop and leaving with a flat-screen television under their arms.

Many of the looters have not bothered to cover their faces as they raided electrical stores, sports shops and off-licences.

Some have even posed for a picture afterwards, proudly showing off their haul and posting the images on social-networking sites.

Prof John Pitts, a criminologist who advises several London local authorities on young people and gangs, says some of those taking the lead in the looting will be known to the authorities, while others are swept along.

Image caption Rioters have set fire to cars and buses

He says looting makes "powerless people suddenly feel powerful" and that is "very intoxicating".

"The world has been turned upside down. The youngsters are used to adults in authority telling them they cannot do this or this will happen. Then they do it and nothing happens."

He says a large number of youngsters are involved in these riots because it is the school holidays and the nights are longer.

Numbers are all important in a riot and the tipping point comes when the rioters feel in control, he adds.

"You cannot riot on your own. A one-man riot is a tantrum. At some point the bigger crowds confronting the police realise that they are in control."

Psychopathic tendencies

Psychologists argue that a person loses their moral identity in a large group, and empathy and guilt - the qualities that stop us behaving like criminals - are corroded.

A social psychologist's view For most people looting is opportunistic. And greed is certainly a factor. But some people approach this situation not necessarily with bad intentions. They are swept away by the crowd, for a variety of reasons highlighted by social psychologists. One concept is called deindividuation. Normally people's behaviour is guided by their own identity and values, which tell us to not do certain things - like taking things without paying for them. But in some situations they take on the values of the group. Our own internal values and norms become less salient. The second idea is called emergent norm theory. Most of these people have probably not been in a riot like this one before. They are unsure of what the appropriate behaviour is. So they look at what other people are doing. And if other people are doing this, it suggests it's normal. Or at least maybe it is something that I can get away with. Source: Jason Nier, associate professor of psychology, Connecticut College, speaking to BBC World Service

"Morality is inversely proportional to the number of observers. When you have a large group that's relatively anonymous, you can essentially do anything you like," according to Dr James Thompson, honorary senior lecturer in psychology at University College London.

"Part of that is down to safety in numbers. There may only be 20 or 30 people who are leading the trouble but the presence of several hundred onlookers makes it far less likely they'll get caught."

He rejects the notion that some of the looters are passively going with the flow once the violence has taken place, insisting there is always a choice to be made.

Watching people getting away with it can act as a motivation for others to start looting, says psychologist Dr Lance Workman.

"Humans are the best on the planet at imitating. And we tend to imitate what is successful. If you see that people are walking out of a shop with a widescreen TV and trainers, a certain kind of person thinks why shouldn't I do that?"

Workman argues that some of those taking part may adopt an ad hoc moral code in their minds - "these rich people have things I don't have so it's only right that I take it".

But there's evidence to suggest that gang leaders tend to have psychopathic tendencies, he says.

This idea of a mob mentality can be found in football hooliganism. Former Manchester United hooligan Tony O'Neill, says there is a similarity between this week's looting and the football violence he took part in for three decades.

It boils down to the buzz, he says. "It's an excitement. You can't take away that thrill - the roar of the crowd. That sense of a group of men, something's happening."

For most, the motivation is the thrill, with the "free stuff" just a bonus. But not for the ringleaders who manipulate the mob to target high-value shops.

He recalls a rampage through Swiss Cottage in the 1980s when Manchester United fans ended up looting a jewellery store. "The mob itself wasn't looking for jewellers but a few of the bright criminals used the mob and bystanders and the mob joined in because of the buzz."

'Just thuggery'

For law-abiding citizens setting fire to a bus or stealing from a shop is simply unthinkable. But academics say socio-economic factors cannot be left out of the equation.

Dr Paul Bagguley, a sociologist at the University of Leeds, says young men are usually engaged in confrontation with the police, while looters tend to include young children and women.

"It's very likely that a lot of people stealing the stuff would not have done it before. There's a sense in these situations that the normal rules don't apply."

He says while looting occurs in most riots, it has dominated this week and they could be called the "consumer society riots".

"If you compare it to the riots in the 1980s, there's a lot more stuff you can loot easily, such as portable electronic gadgets, mobile phones and flatscreen TVs.

"For a lot of looters, it's just opportunity but it also expresses a sense of how else am I going to get a hold of these things?"

Prof Pitts says riots are complex events and cannot be explained away as "just thuggery".

They have to be seen against the backdrop of "growing discontents" about youth unemployment, education opportunities and income disparities.

He says most of the rioters are from poor estates who have no "stake in conformity", who have nothing to lose.

"They have no career to think about. They are not 'us'. They live out there on the margins, enraged, disappointed, capable of doing some awful things."