British English (BrE) is a variant of the English language, spoken mainly in the United Kingdom. Along with American English, British English is one of the main variants taught in most ESL/EFL programs.
Bear in mind, however, that here is, in fact, no single British English variation of English. Instead there are a considerable number of variations mainly found in different locations. Thus, for example, there is:
Varieties of English Grammar - a list of grammar differences between British English and other types of English.
Varieties of English Vocabulary - a list of vocabulary differences between British English and other types of English.