The days in Britain when men referred to or introduced each other by their surnames, when office hierarchies were minutely calibrated by the use of the prefix 'Mr' or 'Miss' are long gone. Informality is the order of the day and first names are becoming de rigueur; even in professional situations, when dealing with doctors, lawyers, policemen, bank managers, informality is being adopted.
The use - or not - of first names still remains generational; the older you are, the more you think it natural to be Mr, Mrs or Miss; the younger you are, the more unimaginable this seems. For many older people the easy adoption of the first name is seen as offensively over-familiar.
The use of first names is meant to imply intimacy but this has become a cheapened currency when used, for example, by waiters. "Hello-my-name-is-Terry-what-can-I-get-for-you-this-evening?" trotted out in a monotone, actively puts a distance between you and him. Don't confuse natural courtesy with the packaged, processed wholesale adoption of over-familiarity: waiters, call centre operatives and salesmen are not aiming to be your friends, so why are they telling you their first names and calling you by yours?
In many parts of Britain you may be called by catch-all 'affectionate' names, which have been part of the currency of communication for many centuries. Do not be offended, this is quite normal. For example, you may be called dear, dearie, flower, love, chick, chuck, me duck, me duckie, mate, guv, son, according to your sex, age and location.
There is much to be applauded here - empty formal conventions are alienating and impede communication. But traditional failsafes are very useful when you find it difficult to judge the social climate. If in doubt, opt for formality.
Nevertheless, if you have erred on the side of informality, remember that it is better to have agreeable manners and call someone by their first name, than be rude to someone while rigidly adhering to correct form and using their surname.