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. Constantine neither enjoyed his legal studies, nor found the work easy, but was determined to prove he could succeed. His wife kept him motivated, restricted visitors to avoid distractions and forced him to study, making him continue when he was several times tempted to give up. The family moved to London in 1949; between 1950 and 1954, Constantine passed the required series of examinations, and in 1954 he was called to the bar by the Middle Temple. Having turned down an offer in 1947 to return to his old employer, Trinidad Leaseholds, in 1954 Constantine agreed to join the same company as an assistant legal advisor. Uncertain about going back to Trinidad and Tobago after living for 25 years in England, he nevertheless believed it was a good time to return, particularly as his daughter was moving there to marry. Before leaving England, he published his book Colour Bar (1954), which addressed race relations in Britain and the racism he had experienced. It also discussed worldwide racial oppression and how the lives of black people could be improved. At the time, according to Peter Mason, this was "an explosive, challenging, hard hitting tome, the more so because it came not from a known black militant but from someone who seemed so charming, so unruffled, so suited to British society". Although not viewed as radical by black audiences, it was aimed at white British readers. The British press gave it mixed reviews and criticised him for unfairness in parts of the book; other critics accused him of communist sympathies. Return to Trinidad and Tobago When Constantine returned to Trinidad and Tobago in late 1954, he found a growing desire for independence from Britain. At Trinidad Leaseholds he felt isolated from other, mainly white, senior staff; this drew him towards political involvement. Eric Williams, leader of the newly