Ms Wagner, who is now co-director of the festival with her sister Eva Wagner-Pasquier, said : "I have decided to hand Wolfgang Wagner's estate to the Bavarian state archive, in the near future, so that access by researchers to these documents is made possible."

She said she had rarely spoken to her father about the Nazis. "He always said, 'We can be very happy that we lost the war,' " she said in an interview with Der Tagesspiegel newspaper. "He had a very negative attitude to the Nazi regime and was happy that he was injured as a young man, and therefore got sent back from the front and survived."

The composer's family has come under intense pressure to be more transparent. Last week, a prominent German historian accused them of blocking access to archives.

Hannes Heer said Ms Wagner had declined to let him examine her father's estate. Ms Wagner said this was, in effect, due to an organisational error. "Despite intensive efforts it was not possible to arrange contact at the right time. Therefore Mr Heer could not get access, which he justifiably complained about," she said.

The historian said there were still "huge gaps" in the Wagner family's historical record, particularly during the Nazi era when the festival was run by the composer's British-born daughter-in-law, Winifred.