However, troubling questions about the company's past forced Mr Middelhoff to set up an independent commission of academics three years ago to examine the record.

In Munich on Monday, the commission set out its findings. The study helped explain the meteoric rise of an obscure family-owned provincial publisher, based in the small central German town of Gütersloh. The researchers were stunned to discover that Bertelsmann was the biggest publisher of Nazi texts, bigger even than the National Socialist party's own printing business. It pumped out 20 million books to rally the troops and spread the word. Its support of the party was evident long before the war. In the early 30s, the firm published, for instance, The Christmas Book for Hitler Youth, which tried to bring together a muscular Christianity with Nazi ideology.

In 1921, Heinrich Mohn had taken over the family business, which was a small-time publisher of religious texts and hymn books.

The man, the company and that region of Germany were imbued with a conservative Protestantism that looked forward to a new, strong state that would reinstate traditional "folkish" German values. That outlook fitted perfectly with that of the Nazi party which took power in 1933.

Until 1924, Mr Mohn was a member of the German National People's Party, which was largely taken over by the National Socialists. He also joined a scheme that financially supported the SS.

Although Mr Mohn was never a member of Adolf Hitler's party he was sympathetic to it and saw both an ideological and business opportunity in its rise to power. Some of Bertelsmann's books were censored but not because they were anti-Nazi.

The company outsourced some work and it was in the Baltic states, the researchers found, that slave Jewish labour was used. Professor Frei said: "The whole post-war image of Bertelsmann was built on a perception that was created after the war. It was possible because there was a significant loss of interest [after the war] and loss of understanding."

Reinhard Mohn was not involved with the company during the war but when he returned to Germany in 1946, he took over a firm which had many of the same senior pro-Nazi managers in place. He now says he rarely discussed what happened in the war with his father and was not aware of the details that the researchers have uncovered. Gunter Thielen, the current chairman, said: "I would like to express our sincere regret for the inaccuracies the Commission has uncovered as well as for the wartime activities that have been brought to light."

The company's war time record, along with that of millions of ordinary Germans who collaborated, was quickly swept away after the war. It is only with the distance of time that Germany has felt able to confront its past. Professor Frei said: "After '45, Germans interpreted themselves as the first victims of Nazis. They did not want to accept what they had done before. After such a total defeat, people re-interpret their lives."