Police investigating the case of Josef Fritzl, the Austrian who held his own daughter prisoner for 24 years, today inspected other properties owned by the retired electrical engineer to make sure that he was not holding other captives in similar underground cells.

Meanwhile officials in the small town where the incest and abuse came to light, said that Mr Fritzl's alleged victims - 42-year-old Elisabeth and the six surviving children fathered by him - would be offered new lives and new names, as would her grown-up siblings.

"The name Fritzl has been muddied," said Hans-Heinz Lenze, head of the social services in Amstetten, Lower Austria. He said that the family would "decide its own future."

Elisabeth Fritzl has told police that her father lured her into the cellar of their home in 1984, drugged and handcuffed her, and kept her imprisoned for almost a quarter of a century. The victim of what police called "continuous" sexual abuse, she is thought to have bore seven children, including a boy who died shortly after birth and whose body was burned in a heating furnace.

Police said yesterday that Mr Fritzl had confessed to keeping his daughter captive and fathering the children.

Three of those children, a girl aged 19, and two boys aged 18 and 5, have been locked in the cramped cellar with her since birth and had never seen sunlight until their release at the weekend. The three others - two girls and a boy - were brought out of the cellar and adopted to be brought up by Fritzl and his wife, Rosemarie.

The abuse came to light at the weekend when Fritzl apparently allowed the 19-year-old girl out of the basement dungeon for treatment after she fell seriously ill. Doctors trying to explain her illness then issued an urgent appeal for her mother to come forward.

The young woman, who is thought to have been suffering from severe cramp brought on by lack of oxygen, is being treated at a different hospital to her mother and five siblings who were taken on Sunday, along with Rosemarie Fritzl, to the neurospsychiatric clinic at the Mostviertel Amstetten-Mauer regional hospital.

Doctors and officials said today that the group were being kept in a "protected zone" at the hospital for their gradual reintroduction to the outside world. Paulus Hochgatterer, a child psychologist, said that they were "in a treatment container that can be locked from the inside".

In brief remarks to reporters outside Mostviertel hospital today, Dr Berthold Kepplinger, head of its neuropsychiatric clinic, said of the children and their mother: "They are in surprisingly good shape, considering the circumstances."

Asked to compare their condition with that of Natascha Kampusch, the young Austrian kidnapped in 1998 and held in a basement in the Vienna suburbs for eight years, he replied:

"They are not nearly so articulate as Natascha Kampusch, but have rather been marked by their experience."

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