The independence constitution of 21 September 1981 (based on that of 1 January 1964) vests governmental authority in a governor-general appointed by the UK monarch, a cabinet headed by a prime minister, and a bicameral National Assembly. The cabinet ministers are appointed by the governor-general on the advice of the prime minister. The National Assembly consists of a 29-member House of Representatives elected by universal adult suffrage, and a Senate of eight members appointed by the governor-general (five on the advice of the prime minister, two on the advice of the opposition, and one on the recommendation of the Belize Advisory Council). Parliamentary elections must be held at intervals of no longer than five years. The voting age is 18.