Everyone seems to know that Stephen Fry (actor and author, born 1957) and Captain Mark Phillips (Princess Anne's first husband, born 1948) attended the school.
Stephen Fry and his brother Roger were at the school during my time, but because I was several years older I never noticed their existence and probably they never noticed mine.
Wikipedia's page about Uley mentions that Rik Mayall (comedian and actor, born 1958) is another old boy.
From when I was at the school, I seem to remember that Sir Peter Scott was mentioned as an old boy, but as he was born in 1909 he would have been about 26 when the school was founded. Maybe he was associated with it in some other way?
What is meant by "notable"? I have a rough rule of thumb that people become notable when a page about them appears in Wikipedia. And yet actors of quite modest accomplishments may appear in Wikipedia, while old boys such as Richard Guha and Azad Shivdasani (with very considerable accomplishments to their names) do not. This seems rather unsatisfactory.