One cannot talk about English conversation codes without talking about class. And one cannot talk at all without immediately revealing one's own social class. This may to some extent apply internationally, but the most frequently quoted comments on the issue are English - from Ben Jonson's 'Language most shows a man. Speak that I may see thee' to George Bernard Shaw's rather more explicitly class-related: 'It is impossible for an Englishman to open his mouth without making some other Englishman hate him or despise him'. We may like to think that we have become less class-obsessed in recent times, but Shaw's observation is as pertinent now as it ever was. All English people, whether they admit it or not, are fitted with a sort of social Global Positioning Satellite computer that tells us a person's position on the class map as soon as he or she begins to speak.
There are two main factors involved in the calculation of this position: terminology and pronunciation - the words you use and how you say them. Pronunciation is a more reliable indicator (it is relatively easy to learn the terminology of a different class), so I'll start with that.