[3] Amid the outbreak of the Second World War, he enlisted into the British Army and went on to serve in the 2nd Battalion of the Queen's Own Cameron Highlanders from 1942 to 1946.

Later on became the Principal Private Secretary to Secretary of State from 1950 until 1953, the Head of the Southeast Asia (later Far East in 1953) Department at the Colonial Office from 1952 to 1955, the Deputy Commissioner-General for the United Kingdom in Southeast Asia from 1956 until 1960, the Head of West Indian Department from 1960 to 1961, and lastly the Cabinet Office from 1961 to 1963.

[8] On 31 March, a banquet was hosted at Istana Darul Hana in honour of Dennis White's service and in celebration of Mackintosh's appointment.

[7] During his time in Brunei, he became the country's Chief Scout,[9] and took part in national events such as the Sultan Omar Ali Saifuddein III's birthday celebration on 23 September 1963.

[5] Angus Mackintosh was given the honorary title of Yang Terutama (His Excellency) Dato Seri Utama by Sultan Omar Ali Saifuddien III.