In 1991 he published a painfully honest memoir of his experience, Through Hell for Hitler, which formed the basis of a BBC Timewatch documentary in 2003. The book was not so much an act of atonement. “I can’t say sorry,” he told a Sunday Telegraph interviewer in 2003. “It wouldn’t mean anything. After all this, it would just sound cheap.” Rather, its account of how an ordinary individual can be sucked into a vortex of barbarity was intended as a warning from history.

An only child, Heinrich Friedrich Carl Metelmann was born on Christmas Day 1922 into a working-class family in Altona, an industrial town near Hamburg. His father, an unskilled railway worker, was a socialist. When Heinrich was 11, his Christian youth group was subsumed into the Hitler Youth, of which he was soon an enthusiastic member.

“It was smashing,” he recalled. “For the first time in my life I felt someone. We were poor, my mother made my clothes, so I always felt a bit shabby; and suddenly I had a fine uniform. I’d never been on holiday; now they were taking us to camp by lakes and mountains.”

He attended rallies, where he saw the Führer. “To us, he was the greatest human being in the world. People say he hypnotised us, but we hypnotised ourselves. Often we couldn’t hear what he was saying: we all screamed anyway. We truly thought we were part of a crusade.”

His father, who had fought in the First World War, told him that Hitler’s talk of the glory of war was rubbish, and that Hitler was just a frontman for rich arms manufacturers. “Once he said it was just as well we had been brainwashed, that we would go mad if we knew what we were really fighting for. I wish now I could tell him: 'You were right, I was the idiot.’” Some children reported their parents’ doubts to the Nazi authorities, with the result that they were arrested. Gradually Metelmann’s father began to hold his tongue in front of his son.

As soon as Metelmann was 18, he joined the Army and was sent to the eastern front as a driver in the 22nd Panzer Division. “I was so excited,” he recalled. “I thought: 'Now I can show the Führer what I’m made of.’”

But as they advanced the 1,000 miles towards Stalingrad, Metelmann – who spoke a little Russian – got to know some of the people whose homes he occupied: “I fell in love with a Russian girl, although nothing ever came of it, and for the first time I began to doubt our racial superiority. How could I be better than her?”

His unit was nearly destroyed in the Russian pincer movement at Stalingrad in November 1942, and Metelmann only narrowly avoided being captured. Yet the reversal of the Wehrmacht’s fortunes did not lead him to disobey orders. He recounted an episode when the tank he was driving approached a group of Russian prisoners carrying a wounded comrade. When the Russians took fright and dropped the injured man in the road, Metelmann’s officer ordered him to drive on – so he did. Once, his platoon mowed down some teenage girls they saw running for cover: “They were girls. It’s inexcusable. But we were frightened.”

Nine out of 10 German soldiers who died in the war were killed in Russia – including half of Metelmann’s own class at school. His lowest point came when one of his closest friends was wounded in the snow by fire from a Russian plane. “There was nothing we could do with him. So I held his head in one hand and with the other I took out my pistol.”

Metelmann claimed to have survived through a mix of luck and cowardice, both moral and physical. On one occasion Russian troops destroyed his vehicle, and in the chaos he went to fetch ammunition. He looked back to see Russian tanks rolling over his fellow soldiers. Instead of going back he ran away and hid in a shelter, ignoring the cries of the wounded. “I had no medical skills, I couldn’t save them. When I came out they were covered by snow.”

Eventually he found himself back in Germany where, in the last stages of the war, he joined the defence of a small town on the Rhine. When American forces entered the town he and six colleagues were hiding in a cellar.

Taken prisoner, Metelmann was shipped to America, where his turning point came en route to a prison camp in Arizona, when he picked up a magazine showing pictures of the piles of corpses and walking corpses at the newly liberated concentration camps. Metelmann had swallowed Nazi propaganda that the camps were merely places where “unsocial” elements were made to do a hard day’s work. “At first I said to my mates: 'Look, just because we lost the war, they blame us for everything.’” But when he studied the pictures more closely he realised that they were not fabrications.

Later Metelmann was transferred to England, where he remained a PoW until 1948, working as a farm labourer in Hampshire. By the time he returned to Germany, his parents were dead (his mother from Allied bombing). But it seemed that few of his fellow countrymen had learned the lessons of defeat: “The Germans were so bitter, saying, 'How can this rubbish defeat us?’”

After just four weeks he returned to the farm in Hampshire, where was given his old job back. In 1952 he married Monika, the farmer’s Swiss au pair. Later he took a job as a railway signalman and, on his retirement in 1987, Charterhouse offered him a job as groundsman.

While several of Metelmann’s old army comrades committed suicide, Metelmann joined the Communist Party and CND and became a committed peace activist. In the 1960s he protested against the Vietnam War. In recent years he attended all the Stop the War marches against the invasion of Iraq and protested against the American bombing of Afghanistan.

After his wife died in 1980 Metelmann sat down to write his book. Some reviewers were repelled by his reluctance to admit any more than collective guilt for the crimes in which he participated; but Metelmann explained that he was determined that people should understand the causes of the war and the processes of brainwashing to avoid making the same mistakes again.

Subsequently, a history master at Charterhouse asked Metelmann to give a talk to his students. More invitations followed from schools and colleges. At Eton, his audience included Princes William and Harry. “I got the best questions at that school, which rather surprised me,” he recalled. “They seem to be completely on the mark when it comes to independent thinking, not as Establishment as I thought.”

Henry Metelmann, who died on July 24, is survived by a son and a daughter.