[7] He demobilised in 1948 at which point he matriculated into Corpus Christi College, Oxford, receiving a BA Honours degree in Jurisprudence in 1951.
He defined its field as:[10]"the study of all aspects of man and his handiwork in the regional setting (Cornwall and Scilly), past, present and future.
The development of society, industry and the landscape in our fast changing world is as much of concern … as the history of those vast topics in the recent and remote past.
[5] He retired as Director of the Institute and Professor of Cornish Studies in 1991; he was awarded an Emeritus Fellowship at Exeter by the Leverhulme Trust (1992–94).
[5] Thomas' first archaeological excavation was at the Bronze Age barrow on Godrevy headland, St Ives Bay in 1950, and he initially saw himself as a prehistorian.
After Gwithian, excavations at early Christian sites included Nendrum Monastery, County Down in 1954; a chapel at East Porth, Teän, Isles of Scilly in 1956;[14] Iona Abbey, Argyll in 1956–1963;[15] Ardwall Island, Kirkcudbright;[16] and Abercorn, West Lothian 1964–65.
[5] He was a board member of the Royal Institution of Cornwall and Honorary Librarian of its Courtney Library until 2011,[18] having previously served as its president in 1970–71.
[5] In 1959, Thomas married writer Jessica Mann[29] a week after she completed her Cambridge finals, and they had two sons and two daughters.