If you really give a toot, then you need to get hold of a copy of Debrett's New Guide to Etiquette and Modern Manners (1999) by John Morgan, or one of the collections from his (former) Times column - also available in book format.
He topped himself in 2000, so unless another person with too much time on their hands and (probably) no friend�s, takes up the Olympic torch of pointless objectivity, it is likely to be some time before the world in waiting receives an updated version. Whatever shall we do?