In Lord of the Flies, the origin of the boys is suggested with the mention of the Home Counties. These are the counties in close proximity to London, England: Herfordshire, Essex, Kent, Surrey, Buckinghamshire, Berkshire and Middlesex.
The book takes place in a fictional atomic war, either during WWII or possibly soon afterwards. There are strong parallels with the situation in England during WWII. Major cities were heavily bombed, not for military purposes but to lower morale. During the Blitz, many children were evacuated to the countryside to escape the war. Here, they are being evacuated from Britain altogether.