SIRC - Passport to the Pub Chapter 1: "In bars and cafes in other parts of the world, waiter service can isolate people at separate tables, which makes it more difficult to initiate contact with others. Perhaps many cultures are more naturally outgoing and sociable than the British, and do not require any assistance in striking up a conversation with those seated near them.
The British, however, are a somewhat reserved and inhibited people, and we need all the help we can get! It is much easier to drift casually into a spontaneous chat while waiting at the bar than deliberately to break into the conversation at another table. Like every other aspect of pub etiquette, the no-waiter-service system is designed to promote sociability.
This is very good news for tourists who wish to make contact with the natives. The bar counter in a pub is possibly the only site in the British Isles in which friendly conversation with strangers is considered entirely appropriate and normal behaviour."
This is particularly magnificent. It goes on to describe just how the 'invisible queue' forms at the bar, and the means we employ to get the barmaid's attention.