- Barrister, Blackstone Chambers (to 2010)
- Appointed to Silk (from 1979)
- Professor of International Law, London School of Economics (from 1976 to 1980)
- Reader in Public International Law, Inns of Court School of Law (from 1973 to 1976)
- Pupillage at the Bar (from 1967)
- Fellow and Tutor in Law, Wadham College, Oxford and Lecturer, University of Oxford (from 1963 to 1976)
- Called to the Bar, Gray's Inn (from 1958)
- Lecturer, Nottingham University (from 1957 to 1963)
- Graduate Student, King's College, Cambridge (from 1953 to 1957)
- Undergraduate, Hertford College, Oxford (from 1950 to 1953)
- Distinguished Fellow, All Souls College (from 2004 to 2010)
- Emeritus Fellow, All Souls College (from 1999 to 2004)
- Chichele Professor of Public International Law and Fellow, All Souls College (from 1980 to 1999)
- Commander of the Order of Merit of the Norwegian Crown
- Honorary Member, Indian Society of International Law (2009)
- Honorary Member, American Society of International Law (2004)
- Honorary Degree, University of Padua (2001)
- Panel of Conciliators and Panel of Arbitrators, ICSID (World Bank) (from 1988 to 1998)
- Bencher, Gray's Inn (1987)
- Delegate of University Press (from 1984 to 1994)
- Member, Institute of International Law (from 1985 to 2010)
