For some reason, we generally classify much of our literature in America similarly to literature involving England.
For example, we study British Literature in high school and college and American Literature in high school and college, but don't really push the others. We often lump them into World Literature, meaning a focus on translated work from other languages or pieces from authors with foreign backgrounds.
William Golding is indeed British. I think our shared language (English) is what has given us the idea to maintain a certain set of study devoted to British Literature. It is also where we derived our language and literary purpose.
I would say no, it is not world literature.
"World Literature" usually describes novels, short stories or poetry from all around the globe - other than the country that is referring to it. So for example, the book "Lord of the Flies" by William Golding might be considered as world literature in countries other than England which is the native country of the boys. Conversely, that book might not be considered world literature in England. By the same token, books from ethnically diverse and varied locations around the world probably qualify to be called world literature when referred to in England. Here, authors such as Maya Angelou, Dostoyevsky, Chekov, Jean Paul Sarte, John Banville or J D Salinger might be referred to as world literature.