Stephen Alexander was a 22-year-old subaltern in the Hertfordshire Yeomanry when he arrived in Singapore in January 1942 on board the troopship Mount Vernon. Japanese aircraft were already bombing Singapore with impunity and his last sight of the ship was of RAF ground staff going up the gangplanks he had just come down. Duff Cooper (Viscount Norwich), Singapore’s newly appointed commissioner, and his wife had just left by air.

In his poignant book Sweet Kwai Run Softly, published in 1995, Alexander wondered if Duff Cooper had forgotten some lines he had written in 1939: “More gladly though would we give all/ That yet we have to give/ Oh, let the old men man the wall,/ And let the young men live!”

“As one of the young men concerned,” wrote Alexander, “it did just cross my mind that it might not have been a bad precedent for a politician, instead of beetling back to resume the role of Whitehall warrior, to share for once the fate of his constituents.”

Alexander stayed on to witness and report on Britain’s most humiliating military disaster with the surrender of 80,000 Allied troops, and one of Japan’s biggest war crimes involving the construction of the Thailand-Burma railway. Under horrific conditions he helped to build the bridge over the River Kwai and survived three and a half years of starvation, malaria, dysentery, jungle ulcers and cholera.

He arrived in Singapore to encounter a general air of demoralisation and the knowledge that after barely a month the Japanese were already halfway down Malaya’s 550 miles of so-called impenetrable jungle. Defeated British forward troops in Malaya were already shambling back in rags across the causeway into the false security of Singapore island. As the Japanese advanced, Alexander joined his regiment manning 25-pounders on the causeway.

One fellow officer observed how down among the “scarlet majors at the base” normality was still a fetish. His arrival at Raffles Hotel, in sweaty field kit, caused such consternation among those dining in mess kit or white tuxedos that waiters put screens around his table. Alexander and his battery were firing right up to the moment of surrender when they were told to destroy their guns.

It was later discovered that the Japanese invaders had only a third of the number of troops of the British, Australian and Indian forces in Singapore.

After confinement in Changi jail Alexander and his regiment were crammed into cattle trucks for a 900-mile journey to the River Kwai to build the bridge. They were accommodated in bamboo huts full of vermin, lice and maggots, with flooded latrines. The task was to build a concrete and steel bridge over the river and the railway alongside it.

The officer in charge of the British PoWs was Colonel Philip Toosey, supposedly the model for Alec Guinness’s portrayal of Colonel Nicholson, the brave but bone-headed officer in the film The Bridge over the River Kwai. Alexander points out in his book that the bridge was never blown up by land and that the association of Toosey, a man of great enterprise and courage, with Nicholson was undeserved.

Toosey, he said, made the best of a bad job and saved very many lives during the building of the bridge and when he ran a PoW hospital. British complaints over their treatment were met by the taunt that the Japanese had never signed The Hague Convention. Fellow prisoners of Alexander were bayoneted to death for trying to escape or died from frenzied beatings for not working hard enough or for concealing radios. “We were told not to complain of sickness as we were told we should be thankful that the noble Japanese had spared our lives at the fall of Singapore, when we were too cowardly to commit hara-kiri.”

After working on the bridge in 1942, Alexander spent an even worse year building the railway in the jungle near the Burmese border. He wrote that his will to live depended on old allegiances, his family and the University of Cambridge, his new friends, a stiff upper lip, a sense of humour and most of all luck. Finally rescue came with the dropping of the atom bomb on Japan. Alexander was repatriated but, like many of his comrades, he felt alienated by life in England. He was therefore happy to accept an overseas post with the British Council and served with it, mainly abroad, for 33 years until his retirement.

His first posting was to Medellín, Colombia, before it became the drug capital of the world. From there he was sent to Tehran, which he left hurriedly after the Prime Minister Mohammed Mossadegh broke off relations with Britain, driving across the desert in the office Ford Pilot to Baghdad, Damascus and Beirut.

He was next posted to Lebanon but left there during the 1958 civil war. This was followed by postings to Hong Kong, British Guiana, Barcelona, Cyprus, just after the Turkish invasion, Turkey and India. Alexander was a gifted theatre director and in all his postings staged plays and musicals.

Stephen Alexander was born in Bristol in 1919, the youngest of eight children. He was educated at Clifton College and went on to Peterhouse, Cambridge, from where he volunteered for the Army at the outbreak of war.

The marriage to his first wife, Germaine van der Wyck, was dissolved. He was married to his second wife, Ruth Thomas, in 1984. He is survived by two sons and a daughter from his first marriage, and by his second wife.

Stephen Alexander, wartime soldier and British Council officer, was born on October 3, 1919. He died on June 14, 2009, aged 89