Papers relating to his life and career, 1924-1971, principally comprising papers relating to his work as British Ambassador to Jordan, 1956-1959, including newspaper cuttings concerning the termination of the Anglo-Jordan treaty of 1948, 1956-1959, and correspondence relating to the stationing of British troops in Jordan, 1958; papers relating to his work as Governor, Commander-in-Chief and High Commissioner, Aden, 1960-1963, dated 1960-1970, including his official reports to the Foreign Office on his visits to the Protectorate states, 1960-1962, his correspondence with King Hussein of Jordan, 1960-1962, newspaper cuttings relating to the merging of Aden with the South Arabian Federation of Arab Emirates, 1960-1963; correspondence concerning British policy towards the South Arabian Federation, particularly the withdrawal of British troops from Aden, 1964-1970; his official report to the Foreign Office concerning the trials in Madrid of opponents of the Franco regime, 1950; notes, cuttings and correspondence concerning Britain's policy towards Japan, 1931-1941, and the signing of the Japanese Peace Treaty, 1951, dated 1971-1975; notes on Australian personalities and contacts written for Sir Morrice James, Johnston's successor as High Commissioner of Australia, 1971; drafts,typescripts, correspondence and reviews of published memoirs The view from Steamer Point (Collins, London, 1964), Mo and other originals (Hamilton, London, 1971) and The brink of Jordan (Hamilton, London, 1972); notes and fragments of unpublished memoirs, dated 1936-1985, mainly relating to his service in the Foreign Office, 1936-1939, Japan, 1939-1942, and Australia, 1965-1971. Photographs, [1938]-1971, principally comprising official photographs relating to his service in Jordan, Aden and Australia. Papers relating to published and unpublished poetry and translations, principally comprising drafts of For Leagros and other poems (Basil Blackwell, Oxford, 1940), Towards Mozambique and other poems (Cresset Press, London, 1947), Estuary in Scotland (privately published, 1974), Poems and Journeys (Bodley Head, London, 1979), Rivers and fireworks (Bodley Head, London, 1980), Talk about the last poet (Bodley Head, London, 1981), Choiseul and Talleyrand (Bodley Head, London, 1982), The Irish lights (Bodley Head, London, 1983) and translations of Turgenev, Pushkin and Lermontov.

Papers relating to the RAF Levies (Iraq), 1955-1959, including typescript copy of speech by Sir Michael (Robert) Wright, British Ambassador to Iraq at the RAF Levies (Iraq) disbandment parade, RAF Habbaniya, 2 May 1955; typescript copy of report to the Air Ministry by Riall entitled 'The Royal Air Force Levies (Iraq) [1955]; typescript 'The RAF Regiment bulletin report on the RAF Levies (Iraq) - the final two years', 15 Jun 1955; typescript 'Iraq Levies - history prior to disbandment', 1955; edition of The Arab World with article entitled 'The Aden Protectorate Levies', Jun 1959. Papers relating to RAF training, 1950-1958, including edition of Air Ministry Restricted booklet 'Manual of ground defence for the Royal Air Force. Volume 1, Active defence', Jun 1950; typescript course notes, Senior Officers Course, Civil Defence Staff College, Sunningdale, Ascot, Berkshire, Feb 1958; typescript notes on nuclear, biological and chemical warfare, Mar-Dec 1958. Papers relating to the Royal Exodus Hunt, Iraq, 1937-1938 and 1953-1954, including correspondence, bills and accounts, May 1937-Feb 1938; manuscript hunting diary and typescript accounts, 15 Nov 1953-7 Feb 1954.