Jamaica slowly gained increasing autonomy from the United Kingdom. In 1958 it became a province in the Federation of the West Indies, a federation of several of Britain's Caribbean colonies. Membership of the Federation proved to be divisive, however, and a referendum on the issue saw a slight majority voting to leave. After leaving the Federation, Jamaica attained full independence on 6 August 1962. The new state retained, however, its membership in the Commonwealth of Nations (with the Queen as head of state) and adopted a Westminster-style parliamentary system. Bustamante, at the age of 78, became the country's first prime minister.