After wartime service in the Royal Artillery, David Summerhayes embarked in 1948 on a diplomatic career, towards the end of which, in the late 1970s and early 1980s, he played an important role as ambassador and leader of the UK delegation to the Committee on Disarmament in Geneva.

His valuable performance in this post earned him further employment with the Foreign and Commonwealth Office for whom he continued for nine more years after his retirement in 1982 as a disarmament adviser.

David Michael Summerhayes was born in 1922, the son of Sir Christopher Summerhayes, who had been a consul in the Levant. He spent his boyhood with his parents in Alexandria, Egypt, and Hamadan and Shiraz in Iran, until the age of 10 when he was sent to school in England.

He attended Marlborough from which in 1940 he was commissioned into the Royal Artillery. As such, he was involved in some of the planning for the “Torch” landings in Algeria in 1942, and he subsequently served with the 1st Army in Tunisia as part of 5th Corps HQ and as a troop commander in 105 Light Anti-Aircraft Regiment.

During this time one of his duties was to form part of the protection for General Eisenhower’s house near Tunis where Winston Churchill was secretly being treated for pneumonia while on his way back from Moscow to London. He subsequently moved with his regiment to the Naples area in support of the US 5th Army.

At the end of the war Summerhayes applied to the Middle East Centre for Arabic Studies and was among its first intake when it was housed in the Arab Quarter of the Old City of Jerusalem. On one occasion, while on leave from the centre, he made a journey by camel across the Sinai desert.

In 1946 Summerhayes followed his father and grandfather to Cambridge, to read a degree to qualify him for entry to the Foreign Office. However, his degree course in history and economics at Emmanuel was cut short in January 1948 by a summons to the Foreign Office where he was to spend the next 45 years.

To get to his first post in Baghdad, he decided to drive from London, crossing the Syrian desert by following the oil pipeline. This was a peaceful period of independence in Iraq under the Prime Minister Nouri al-Said, in the last days before Colonel Abdel-Karim Kassem’s coup in 1958, and he was able to spend time travelling all over the Kurdish region.

He next served in Brussels, 1950-53, and The Hague, 1956-59, where he helped to found the International School and married June van der Hardt Aberson.

His next posting was as first secretary and consul in Reykjavik, 1959-61, in the tense aftermath of the first of the fishing rights disputes with Iceland, known as the Cod Wars. In 1965 the Foreign Office sent him to Buenos Aires as consul-general, and later political counsellor.

His next posting was in South Africa in 1974 as minister. There he led the British team in the complex negotiations that finally brought Namibia to a peaceful independence.

It was in the final period of his career that he made his most significant contribution to international diplomacy in the postwar period. As head of the FCO’s arms control and disarmament department from 1970 to 1974 and (after his four years in Pretoria and Cape Town) ambassador leading the UK delegation to the UN Committee on Disarmament from 1979 to 1982, he played a leading role in setting out Britain’s arms control policy.

He was an influential negotiator in the formulation of the Biological Weapons Convention and he led the British delegation to the 1980 Non-Proliferation Review Conference.

In an atmosphere of international concern over the spread of nuclear weapons against the background of continuing rivalry and suspicion between the West and the Soviet bloc, he believed in maintaining a level-headed relationship between defence and negotiation. During long meetings at the UN, his patience, good humour and diplomatic skills were well deployed.

His clarity of thought, calmness and courtesy in his firm handling of the British interest earned the respect not only of his US colleagues but of the Soviet side as well.

At his farewell dinner in Geneva, the ambassador Victor Israelyan, his Soviet counterpart, told Summerhayes that when teaching students at the foreign affairs school in Moscow he used him as a model of the attributes that they would need if they were to become successful negotiators.

After his official retirement he was appointed in 1983 to a new post as disarmament adviser to the FCO.

In a period when debate in Britain on nuclear weapons was at its height, his role was to travel the length and breadth of Britain talking to peace groups, churches and other organisations, to persuade people that the Government’s defence and nuclear policy was the right one and that nuclear weapons had to be maintained.

After the collapse of the Warsaw Pact in 1991, he was particularly proud to go with a Nato colleague as the first representatives of the West to tell the Soviet War College in Moscow that Britain and Russia were no longer adversaries. Summerhayes had been appointed CMG in 1975.

He is survived by his wife, and by two sons and a daughter.

David Summerhayes, CMG, diplomat, was born on September 29, 1922. He died on November 12, 2008, aged 86