In October 1939, having returned to South Africa, he travelled back to England hoping to join the army, but was rejected on medical grounds, because, since the age of 11, he had been lame, with a knee he couldn't bend due to an injury from a cricket ball that caused osteomyelitis.
[1] He went on to join HM Diplomatic Service in Basutoland in 1941 where he served as an Assistant District Officer before becoming Private Secretary to the High Commissioner, Sir Evelyn Baring, in Cape Town in 1946.
Duncan's approach to development in Africa was broad as well as original: he believed that soil erosion was a major issue of land management and published a pamphlet on this subject, entitled "The Enemy", in 1943 (Morija: Lesotho), under the pseudonym 'Melanchthon', Greek for 'black earth'.
Fourthly, he always had an intense feeling of personal destiny, partly as the consequence of his father's career, which had culminated in his being Governor-General of the Union of South Africa.
At this point he was working closely with the Congress movement, but soon considerable mutual distrust developed as a result of his suspicions that the ANC was being manipulated by members of the South African Communist Party, which had been secretly revived in 1953.
The defeat of the campaign and the banning of the African political movements contributed to Duncan's growing disillusion with solely non-violent opposition to apartheid.
However, in 1965 he was dismissed from his post: the reasons given included the fact that he had sent a personal letter congratulating his old friend and colleague, Chief Leabua Jonathan, on winning the Lesotho general election (the PAC was allied to Leabua's opponents, the BCP); and that, without waiting for an accord from Headquarters, he had recognised the new Government of Algeria formed by Houari Boumedienne after his coup d’état in 1965.
[10] However, Duncan remained a PAC member, and he took the decision to stay in Algeria, where he found work within a relief organisation, Comité Chrétien de Service en Algerie, part of the World Council of Churches.
[11] During the years 1964-7 he deepened the ideas he had first expressed in The Enemy in 1943 about the effect of humans on what is now called 'biodiversity', and wrote Man and the Earth[12] (published posthumously in 1975.).
This analysis of the way people exploit the planet had a breadth which was exceptional at the time, and covered detailed issues in politics, history and science.
[13] This scholarly work is remarkable since it proposes an approach to dealing with the challenges at a prescient date (the mid-1960s), and at a time when Duncan might have been preoccupied with the more immediate struggle against apartheid.