One of the important ideas that Golding wanted to bring out, was the idea that British boys would be no different from anyone else when it came to their ability to become savage and violent. Lord of the Flies was in some ways a direct response to books like The Coral Island, in which the British boys were differentiated from the "natives" and were able to maintain all their civilized ways despite not being subject to the rule of law, etc. in the way they were used to.
So Golding wanted to demonstrate that even British boys, trained in all the ways that British boys were trained, were also subject to the same tendency towards evil, the same ability to descend into savagery that any other boys would be. He wanted to make a break from the idea put forth in The Coral Island and other texts that British boys were somehow inherently different from "natives" or other races and nationalities.