Dafydd Jenkins was the major authority on the laws of the 10th century Hywel ap Cadell, or Hywel Dda, the only king of Wales to be given the epithet "Good".
Jenkins put together a composite text from manuscript sources dating from the early 13th century and threw a great deal of light on the complexities of its language and meanings.
As well as a number of studies in Welsh, he published the fruit of his research in Celtic Law Papers (1973), Hywel Dda and the Law of Medieval Wales (1985), and The Law of Hywel Dda (1986), and (with Morfydd E Owen) edited The Welsh Law of Women (1980), a Festschrift presented to Professor Daniel A Binchy. These books demonstrated that the Laws, as well as being one of the chief glories of medieval Wales, are also valuable material for students of social history, anthropology, jurisprudence and comparative law.
Bringing to this work the expertise of a professional lawyer, Jenkins also made a lucid and, for the first time, an accurate translation of the texts which took into account the anonymous authorship and literary quality of medieval legal prose and pointed to the implications the Laws had for the literature of the period, notably the Welsh prose masterpiece known as The Mabinogion.
Above all, he demonstrated that one of the strongest features of the Welsh language was the technical vocabulary of the law-books, in particular its rich store of abstract nouns and incredibly flexible syntax. The books are an invaluable source of evidence about the nature of medieval Welsh society, from the king's court through the professional classes of priest, physician and poet to the rules governing marriage, divorce, property, theft and murder.
Dafydd Jenkins was born in London on St David's Day 1911 but brought up by Welsh-speaking parents from Cardiganshire, where he settled in 1938. After Merchant Taylors' School, he read Natural Sciences and Law at Sidney Sussex College, Cambridge, was called to the Bar at Gray's Inn in 1934 and was practising as a barrister on the South Wales circuit in Carmarthen at the time of "the Fire in Llyn" two years later.
This act of arson, carried out by leaders of the fledgling Plaid Cymru, was a protest against the building of an RAF bombing school on the land of Penyberth, a house significant in the history of Welsh Recusancy. All constitutional means of preventing the development, including the support of all the Welsh MPs and county councils, had failed. On the night of 8 September 1936, huts and building materials were set alight by three Nationalists, after which they reported themselves to the police. A trial at Caernarfon Assizes failed to reach a verdict, and at the retrial, at the Old Bailey they were sentenced to a term of imprisonment. The case caused outrage in Wales and had a profound and lasting influence on the country's cultural and political ethos.
Jenkins, an active member of Plaid Cymru, wrote an authoritative account of the incident in Tdn yn Llyn (1937, translated into English by Ann Corkett as A Nation on Trial in 1998). He also worked unstintingly as Secretary of the National Language Petition of 1938 which collected 400,000 signatures in support of a request to the British government that Welsh be granted a measure of official status in the public life of its own country, a concession that was not wrung from it until 1967.
As a literary journalist between 1936 and 1942 Jenkins was closely associated with the magazine Heddiw (Today). It discussed Welsh Nationalism from a left-of-centre point of view and in its editorials took the Republican side in the Spanish Civil War. It devoted a great deal of space to pacifist arguments based on the Catholic concept of "the just war" which was greatly agitating many intellectuals in Wales.
For a while during the 1930s, as the right-wing Saunders Lewis tightened his grip on Plaid Cymru's policies, Jenkins grew ever more uncomfortable. He believed the party should make a direct approach to Welsh Socialists, whom he believed might respond to the case for national self-determination: "Wales cannot be won for Home Rule unless the Socialists of Wales are won over", he wrote in The Welsh Nationalist. He nevertheless remained a Plaid Cymru member and continued to play an active role in its affairs.
During the Second World War Jenkins, a committed pacifist on Christian grounds, registered as a conscientious objector and was ordered to work on the land. This was his introduction to the tradition of agricultural co-operation which had long been practised in Cardiganshire.
Jenkins played a prominent part in the Parliament for Wales Campaign launched in 1951. A quarter of a million people declared themselves in favour of an elected, legislative Parliament but the initiative failed. He was also a keen member of the Welsh Academy, the national association of writers in Wales, and was contributing vigorously to its journal, Taliesin, in his 90th year.
An accomplished writer in Welsh and English, Jenkins won the Prose Medal at the National Eisteddfod in 1946 with a volume of literary criticism and published two books about Denmark and Sweden, where he visited frequently.
Jenkins joined the law department at Aberystwyth in 1965 and held a personal chair in legal history and Welsh law from 1975 until he retired in 1978. For many years he was a leading member of the colloquia on Welsh medieval law held at the constituent Colleges of the University of Wales, and among his colleagues he was generally considered to be the doyen. A somewhat formal, perhaps shy man, he gave generously of his erudition to younger scholars.
Dafydd Jenkins, barrister and scholar: born London 1 March 1911; Lecturer in Law at the University College of Wales, Aberystwyth 1965-75, Professor of Legal History and Welsh Law 1975-78 (then Emeritus); married Gwyneth Owen (one son); died Blaenpennal, Ceredigion 5 May 2012.