in 1947 constantine became chairman of the league of coloured peoples, a position he held until the league was discontinued in 1951. in 1948 he was elected president of the caribbean congress of labour, and between 1947 and 1950 was a member of the colonial office's colonial social welfare advisory committee. also in 1950, he became involved in a controversy over the interracial marriage of seretse khama, the future president of botswana. constantine lobbied the government on khama's behalf, organised meetings and even approached the united nations. little was achieved, and constantine disapproved of the approach of the labour government and its prime minister, clement attlee, but declined an opportunity to become a liberal parliamentary candidate.