The British consider politeness to be very important.  For instance, it would be rude to ask for or receive anything anywhere (including a ticket office or shop) without saying 'please' and 'thank you' It would also be considered rude to bump into someone accidentally without saying 'sorry', or to push past without saying 'excuse me'.  Politeness also demands that you queue in an orderly line when waiting to be served in a shop/bank/restaurant etc. or when waiting for a bus.  Any attempt to jump the queue will invite criticism or hostility from the other people waiting.

The British understanding of politeness does not require elaborate greetings or preliminaries to the main subject you wish to talk about.  In fact, doing this can be seen as a waste of time and may irritate the person you are talking/writing to.  Make a brief, polite introduction and then say what you want.  This advice applies even more to examinations, both verbal and written, where a failure to answer a question or deal with a subject directly may be interpreted as a lack of precise knowledge.

In the interests of politeness British people often make formal remarks that they do not mean literally, and it would be a mistake to interpret them literally.  If, after a brief meeting, a stranger says to you 'you must come and have dinner some time', this is only to be interpreted as some vague intention on the spur of the moment, an expression of their having found you pleasant and/or interesting to talk to.  If they really want you to come they will invite you for a particular day and time.  Beware: mis-reading coded politeness can cause acute embarrassment!

By and large British people avoid physical contact with strangers beyond a handshake on their first meeting - embracing, kissing, holding hands/arms etc. are reserved in the UK for situations of familiarity or sexual intimacy.  British people also like to keep a minimum physical distance apart from each other when holding a conversation.  Observe how they behave and try to do the same - if you get too close you can cause embarrassment or discomfort.  If you are introduced to a stranger, 'Pleased to meet you' is the usual courtesy; 'Nice meeting you' can also be said on parting.

It is usual in Britain to give advance notice of your intention to visit people (phone first!), though amongst young people this is not so strictly observed.  If you are invited to visit or stay with a British family it is important to say whether you can accept (especially if the letters RSVP appear on the invitation) and then to be punctual.  If you are going to be late you should let your host know in advance.  It is customary to take a small gift as a sign of appreciation, e.g. some flowers or chocolates.  If you have stayed for several days as a guest then it is usual to give a small present either when you arrive or are about to leave.

Usually you will get to know people on first name terms quite quickly - if in doubt, continue to use the surname (family name), with the title Mr, Mrs, Miss, Ms, Dr, Professor.  Older people or those with whom you have a more formal relationship may prefer you to use surnames.  Be warned that when somebody such as a lecturer or supervisor asks you to address them by their first name, this does not necessarily indicate that they are treating you as a friend.  Strangers to the UK are sometimes puzzled or hurt to find that they are treated formally as a client or student by the same person who insists on the use of first names - informality has itself become a formality!  This is not unusual and not directed at you personally.

While politeness is highly prized, flattery is not.  British academics do not expect their opinions to be accepted without question and will respect students who put forward their own point of view in a polite, reasoned way.  Beware in particular of using exactly the same words as your teachers or source books in essays, exams, etc. - this may be taken as evidence that you have not properly understood, or even of plagiarism.