Sir Donald Logan was a familiar figure in diplomatic circles, having served as Ambassador to Bulgaria in the early 1970s before ending his diplomatic service career as the leader of delegations to two long conferences, concerning the law of the sea and the protection of Antarctica. He then went on to direct the Great Britain/East Europe Centre for seven useful years.

However, his name is more widely remembered for his brief but central involvement in a bizarre diplomatic excursion: the France-British-Israeli meeting at Sèvres in October 1956 which settled the terms of these three countries’ clandestine co-operation in the Suez affair.

The year 1956 was an extraordinary one in which to be thrust into the centre of British foreign policy-making. In the summer Sir Anthony Eden, the Prime Minister, with an unhappy Selwyn Lloyd, Foreign Secretary, bobbing in his wake, set out to topple President Nasser and restore Britain’s eroded position in the Middle East.

Eden’s obsession drew him into ever closer involvement with France and Israel and at cross-purposes with the United States. Taking direct control himself, he excluded most of the Cabinet and Whitehall from the central reality of British Middle East policy. The staff of the Foreign Office were left to guess at what the Prime Minister was about.

Logan found himself abruptly translated from outsider to insider when Eden dispatched Lloyd to the secret tripartite meeting at Sèvres on October 22, 1956. Logan was with Lloyd at an engagement outside London when the Prime Minister called. It was natural for him to accompany his chief to Paris. Thirty years later he described the occasion in a long article in the Financial Times, doing so in terms that were typical of the man: factual, balanced and unopinionated.

The Israeli delegation at Sèvres included David Ben-Gurion, the Prime Minister, General Moshe Dayan, the Chief of Staff, and Shimon Peres, Foreign Minister and Director-General of the defence ministry. The French team was led by its Prime Minister, Guy Mollet, and included the defence and foreign ministers.

Three copies of a document that became known as the Sèvres Protocol were produced, one for the British, one for the French and one for the Israelis. It was evisaged that the Israelis would launch a raid on Nasser’s Eqypt, giving British and French forces a pretext to occupy land around the Suez Canal and so keep it from Egyptian control. Eden, who long denied the existence of the meeting, and of any collusion, is thought to have ordered the destruction of the British copy of the protocol.

In his own account, Logan included only one personal judgment, and that a contemporary one, drawn without benefit of hindsight. He told how Lloyd, obviously disconcerted by the company he was keeping, drew Logan aside to ask him how he thought the Arabs would react to the military charade that was being prepared. Logan replied that they would be surprised, but might accept the situation if the operation was completed quickly. It was a shrewd judgment, if an unadventurous one; but one of the many tragedies of Suez was that, for all their collusive preparations, the British and French singularly failed to get the thing done quickly.

Logan returned to London with his chief that night, but he was twice sent back to Paris, the first time alone, essentially to try to ensure that no trace of the collusion should enter the official and eventually the historical record. So of the three Britons involved in the Sèvres affair — Logan, Sir Patrick Dean and Lloyd himself — only Logan was present for all three acts of that mysterious drama.

Donald Arthur Logan mixed the conventional and unconventional throughout his career. Born in 1917, he was denied a university education by war, but he became a Fellow of the Chartered Insurance Institute the year war broke out. He served throughout it, in the Royal Artillery and on the British defence staff in Washington. The foreign service, which he joined in 1945, employed him on two tours of duty in London and sent him to Tehran and Kuwait, before recalling him at the age of 37 to serve as assistant private secretary to Selwyn Lloyd.

After Sèvres Logan stayed with Lloyd for two more years and then served for two years in Washington. In 1960, at the age of 44, he was appointed Ambassador to Guinea in West Africa. After two years with a command of his own, however small, he was brought back to London and then dispatched to Paris as information counsellor. There, as in London and Washington, he was relatively a small cog in the machine. In 1970 he again got a mission of his own, in Sofia, Bulgaria, but three years later he was back in a subordinate position, as deputy head of the British delegation to Nato.

These shifts, between large missions and small and between command and subordination, would have unsettled some of his colleagues, but Logan plodded imperturbably on, and rounded out his career with four years’ service as the leader of British delegations to two long conferences convened to address new issues — the codification of the law of the sea and the protection of Antarctic maritime resources.

In 1976, referring to disputes that might emerge over the law of the sea, Logan called for a flexible system that allowed states to chose between the International Court, a special tribunal or “ad hoc arbitration”.

Writing in 1984, he said that he could confirm from recent observation that Antarctica is “still” a vast beautiful wilderness, the domain of its wild beasts and its scientists. Had there been no Antarctic Treaty, he added, it might have been different: “As the relics of old whaling stations there testify, the presence of man and the dynamic of his activity are a reality and necessitate protective management if the nature and the peace of Antarctica are to be preserved. Environmental protection is the foremost consideration.”

Logan retired from the Diplomatic Service at the age of 60, but he went on to serve for seven years as director of the government-funded but independent Great Britain/East Europe Centre.

These were almost the last years of communist power in Eastern Europe. Opportunities for the centre to build increased unofficial contacts between Britain and the countries of the area multiplied; Logan, with his Bulgarian experience and steady methodical style, was able to contribute much. Some watching him at work felt that the centre brought him the solid if modest achievement that his rather bitty Diplomatic Service career had denied him.

Logan was appointed CMG in 1965 and KCMG in 1977 at the end of his time as leader of the Law of the Sea Conference delegation.

In 1957 Logan was married to Irène, the daughter of a Belgian diplomat. He is survived by her, one son and two daughters.

Sir Donald Logan, KCMG, diplomat, was born on August 25, 1917. He died on October 23, 2009, aged 92