Do you really want to know about British insults? I do not know why you should teach such expressions, but I can only advise an article https://www.anglotopia.net/site-news/featured/british-english-the-top-50-most-beautiful-british-insults/. There are top 100 best expressions used by native speakers. Perhaps with this article you can learn more about the language, so you can read the article or even learn these phrases to use