Hitler concealed huge income from speeches and his book Mein Kampf

He owed the authorities 405,500 Reichsmarks (6m euros; £4m in today's money) by 1934, when as German chancellor his debts were forgiven.

A retired Bavarian notary, Klaus-Dieter Dubon, found Hitler's tax secrets in papers from the Bavarian State Archive.

"He was constantly challenging tax office rulings," Mr Dubon told Reuters.

The tax office inquired how Hitler had obtained funds to buy a luxury Mercedes car while he was in prison following his abortive 1923 coup attempt.

Hitler replied that he had received a bank loan and the car "is for me just a means to an end".

After his release from jail, Hitler had declared his possessions simply as one desk and two bookshelves, the German newspaper Bild reported.

Mein Kampf earnings

Mr Dubon told Reuters that Hitler had earned 1.2m Reichsmarks in 1933 from sales of his book Mein Kampf - "a huge income, when you consider teachers then had annual salaries of 4,800 marks".

But he failed to pay tax on 600,000 Reichsmarks of that income, the researcher found.

By 1945 Hitler had made 7.6m Reichsmarks out of Mein Kampf, without paying any tax.

In his lengthy correspondence with tax inspectors, Hitler repeatedly asked to pay in instalments.

But once installed as chancellor in 1933, his tax troubles were over.

He was declared free of tax obligations in 1934 and the reward for the official who absolved him was a monthly tax-free income of 2,000 Reichsmarks.

"It's all so ridiculous," said Mr Dubon. "But in a dictatorship everything the dictator does is correct."