An Austrian man who imprisoned a secret incestuous family in his basement for nearly a quarter of a century “managed to deceive everyone" over their existence, police said today.

Police said Josef F kept his daughter Elisabeth locked up in a windowless cellar beneath his home while he fathered seven children by her. He has also confessed that he burned the dead body of one of the children.

Officers today described the 24 years of abuse as the worst crime in the history of the country. Six of the children have survived their ordeal. Three lived upstairs with Mr F and his wife Rosemarie, while the others had not left the cellar or experienced daylight until this weekend.

Despite adopting three of the children Mr F’s wife was unaware of the horrors hidden within her own home, police spokesman Colonel Franz Polzer said.

It is understood that the father was able to convince his wife that three babies were left on their doorstep with letters from their daughter. The mother believed that her daughter had run away from home, in fact she was being held captive below ground.

A seventh child was said to have died three days after his birth. His body was tossed into an incinerator at the family home in Ybbs Street in the town of Amstetten, West of Vienna.

Elisabeth, 42, is now suffering from serious health problems and was today being looked after by police psychologists.

"The mother only had one care, which was not to see the father of her children again and that her children should be looked after by others,” said Mr Polzer.

“The description she gave was beyond the belief of the police officers leading the investigation.

"He pressured her physically to keep her there and sexually abused this young woman, his own daughter, over many years. The result of his criminal activities has been to break this woman.

“This case knows no precedents or comparisons in Austrian history, but I would like to say that in other countries terrible things have happened as well.”

Beneath the family home beyond a hidden electronic trapdoor the children, aged 19, 18, 16, 14, 11, and 5, were conceived and born.

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