From the BBC:
Buying drinks in rounds can damage your health, says the Scottish Executive. But the round is about much more than drinking, it's a complex social activity that keeps the peace.
Getting a round in is a social minefield, with elaborate unwritten rules and punishments for anyone who gets it wrong.
The custom of buying drinks in rounds has been criticised by the Scottish Executive, with a health minister warning that it can pressurise people into drinking too much.
But Dr Peter Marsh, the co-director of the Social Issues Research Centre, says that below the surface the pub round is a complicated, highly-regulated social ritual.
Being in a round means being accepted as a member of a group. And once inside this group, there are rules to be carefully observed about when and how often drinkers should be heading to the bar.
"Buying a round in a pub marks you out as a member of a very specific group - and by watching who buys drinks for whom, and in turn who receives drinks from whom, you get an immediate idea of the social dynamic there," says Dr Marsh.
There is nothing random about how drinks are bought in a round.
“There's a lot of monitoring - because you don't want to buy the drinks too early, you don't want to buy them too late. There are unwritten rules, such as if half the round are towards the bottom of the glass, that's the time to buy," he says.
The greatest social danger is to be labelled as a round dodger who never finds their pocket - on the surface everyone might be smiling, but they're keeping a careful note on the progress of the round. People who don't buy their rounds become ostracised or pushed to the fringes of the group, it makes them extremely unpopular. It's seen as a deviant behaviour not to reciprocate.
"It goes the other way too, as people who buy too many are equally unpopular, as it's seen as showing off," says Dr Marsh.
If it was just about buying drinks, we would be more like the tourists arriving at a pub who all buy themselves an individual drink, says Dr Marsh. The round-buying is a more subtle piece of psychology….
I don’t know if the round-buying culture is entirely unique to Britain, but, like the business of drinking whilst standing up, I’ve not seen it replicated elsewhere as most places favour the tab and final bill method.
For the outsider, being taken out for a drink in Britain must be a social minefield. It’s hard enough for insiders.
For example, when the group is large enough to cross the critical threshold – ie. so large that it is obvious that even at British rates of drinking you’ll never get all the way round so that the first person to buy for everyone will in turn have one drink bought for him by everyone – then there results an delicate shifting and sifting into sub-groups, decided by such factors as closeness of blood relation and length of friendship, approximate rate of consumption, unfinished conversations, balance of designated drivers and intended flirtations.
The matter becomes yet more difficult where one ‘owes’ somebody in the group a drink. It is customary in Britain to dismiss all offers of recompense for any smallish favour with the phrase ‘just buy me a pint sometime’. And then there are those occasions where a friend might have bought you a solitary lunchtime drink and you are now obliged to buy him one back. British men can’t remember birthdays, but they have photographic memories about the people to whom they owe pints, and it is quite common for someone to reciprocate on a pint several years after the initial favour.
Add to this mix the complexities of financial factors: it is understood that poor students, OAPs, or younger siblings should not usually have to stump up for gigantic rounds, while the pressure is on alpha males to buy the early rounds, since they are generally more expensive, as people drop off through the evening, or switch to halves or orange juices (although since designer soft drinks have become as expensive as booze, the teetotaler card doesn’t carry the weight it once did.)
All of these subtle calculations are unspoken but, strangely, are universally understood.