a preppy person is what a UK ya would be in america. A preppy gains their name from going to prepatory school, while a ya is called that due to the way they speak (oh, ya, super dahling)-it is taken for granted that a ya went to private school. The main similarities are that they both tend to be affluent (note, they do not have to be mega-rich), they both tend to be old money with big old houses (ya in south east of england, preppy, north east coast of usa), they both tend to have traditional summer houses that have been in the family for generations (ya in highlands of scotland, preppy in places like marthas vineyard), they both have a fashion uniform (a female ya has to wear a pastel pashmina and have long blonde hair, a male ya has to have a gilet and a pink rugby shirt, a preppy basically has to wear ralph lauren with the collar up).
However there are differences, a ya tends to be much less overtly snobby since they belong to an overtly class loving country that will do it for them. a preppy will probably have more money since inheritance tax is destroying the upper class in the UK and therefore the ya culture.
a ya will tend to think of themselves as better than a preppy since they beleive they dont really count because they are not part of an aristocracy, and basically because they are american. a preppy will think they are better than a ya because they probably know they are richer and because they beleive they made their money and did not inherit it (even though it is in fact daddy that made it)
Ya: Oh, dahling,you simply must come over here and see the estate. its simly wonderful at this time of year!
Preppy: ok, sir/lord/countX il get my dad to prepare the jet.