A constitutional convention convened in London in March 1960 reached agreement on another new legislature, to consist of an elected House of Assembly (35 seats) and a nominated Senate (13 seats). In the ensuing election of 21 August 1961, the PPP won 20 seats in the House of Assembly, entitling it as the majority party to appoint eight senators. Upon the 1961 election, British Guiana also became self-governing, except as to defence and external matters. The leader of the majority party became Prime Minister, who then named a Council of Ministers, replacing the former Executive Council.