My grandfather the Nazi

He is wearing his day clothes - a Nazi uniform. His captain's pips are on his lapels. The Iron Cross is on his breast pocket, just beneath the ribbons of the Cross of Honour - both of them awards he had earned in the bloodshed of the Western Front during the First World War.

At the time of the photograph - possibly May, 1944 - the sight of an SS officer raking leaves in his garden, on an SS estate in Berlin, would have been perfectly normal.

But for Derek Niemann, the photograph is extraordinary. For the man in the uniform is his paternal grandfather, Karl.

Derek has now written a remarkable book about him, called A Nazi in the Family.

Karl was not just a member of the Nazi Party and an SS officer. During the Second World War, his job that meant he visited many of the concentration camps for which the Nazis are forever notorious.

"It took many years for my grandfather's story to come out, that as an SS officer he had been a manager of slave labour in concentration camps such as Auschwitz, Buchenwald, Dachau, Sachsenhausen and many others," says Scots-born Derek.

"For most of his life, my own dad Rudi, who had grown up in Germany then, like his sister Anne, emigrated to Scotland, hadn't told his family anything about his early childhood in Germany.

"Once, he let slip that Karl had been a 'pen-pusher' in Dachau.

"But it wasn't until I was 50 when, searching the internet, I came across my grandfather, and references to what he had done: 'crimes against humanity', ''use of slave labour'."

It was a revelation that Derek has never forgotten, and which, several years later, has now led to his book.

"I suppose Karl was a middle-ranking functionary in the SS," says Derek, an author and nature writer. "My dad had called him a pen-pusher, which made me assume that he had just been a clerk in a wee office, filling out forms. But he was more than that.

"Karl ensured that thousands of concentration-camp inmates were pushed into work. His work meant that he was a regular visitor to such places, and he would surely have been a witness to scenes of unimaginable brutality."

Karl Niemann was born in a small hamlet on April 30, 1893, the youngest of seven children.

He saw action in the Great War and was taken prisoner. He wasn't freed until March 1920, 16 months after the war had ended.

He and his wife, Minna, eventually settled in Dortmund, where they raised a family. Karl worked for a publishing company but was able to land a job with the SS, in Bavaria - he was the auditor for an SS training camp next door to the Dachau concentration camp for political prisoners.

By the time war broke out in 1939, he had become a business manager in the SS Business and Administration Office, in Berlin.

During the war years, as a troubleshooter and quality inspector, he toured all the industrial 'plants' - the concentration camps - that were tied into the SS' woodwork production business.

In 1945, however, his luck ran out. Karl disappeared in a US army jeep, and he spent the next three years in internment in former PoW camps.

In July 1948 he stood before a denazification tribunal. Finally, he was allowed home to his family. But nothing was ever the same for him again.

Says Derek: "I think Karl had a good idea about what was going on during the war.

"He knew, for example, how many Jews were killed on a certain date in November 1942. That sort of information was not known by the general populace but it was known by him, and it must been known by everyone who was working for the SS at that time."

Afterwards, Karl was a broken man. "It's impossible to say for sure, but I don't think he was broken by what he had done. It was more by the fact that everything had gone wrong for him. Germany had lost the war.

"He had lost his son, Dieter, in the battle for Würzburg in April, 1945.

"He had lost his job, he no longer had a status. Two of his children had left for Scotland. I'm guessing that these would have been the principal factors.

"I feel, too, that maybe he distanced himself. He said, 'I didn't kill anyone: I was just doing my job'. But my dad definitely said that when he came back home, he was not the same person."

Derek has also given a lot of thought to Karl's wife, Minna, since writing the book.

"She wouldn't have wanted to have voiced any criticism of the regime, even to her own children," he says. "There was always the risk that little children would go into school and say, 'My mum says this...', and then they would all be straight into the concentration camp.

"I was massively conflicted while researching and writing the book. It was a big trial. Psychologically, it was difficult for me to start. My immediate family were not keen on me doing it. One worry was what the book would do to our relations with my uncle Eki in Germany, but he has been fantastic and very open, saying, 'Go ahead, tell the story'.

"In the book I've tried to be as honest and open as possible."

The war ended in 1945. Ambitious plans have been announced for three days of celebration in May to mark the 70th anniversary of VE Day.

Germany itself has been reunified since 1990. And Karl himself might have approved, his grandson believes.

"Fundamentally, he prized loyalty," Derek says.

"Karl was a man of complicated motivations, He was a strict father but he could be relaxed and garrulous.

"It even emerged that during the war he arranged deals with the Gestapo to have some inmates freed. Some of these inmates spoke in in his favour at his own tribunal, in 1948."

* A Nazi in the Family is published by Short Books at £14.99