With every passing day, the Fritzl case raises more questions about possible failings by the authorities that may have prolonged the horrific events. If gross negligence were established by the police, social services or government departments for failures over records, the family would have the possibility at least of bringing legal proceedings.

The European Court of Human Rights, to which Austria is signed up, has swept away immunities that used to be enjoyed by agents of the State such as the police, where gross negligence is involved.

David Pannick, QC, a leading public law barrister, said: “Article 2 of the European Convention on Human Rights protects the right to life and if authorities have been seriously negligent so as to create a real risk of loss of life or serious harm then legal proceedings can be brought against them.”

The long-standing immunity enjoyed by police in the UK was overturned by the European Court of Human Rights in a case called Osman in 1998. It was brought by Mulkiye Osman and her son Ahmet, who had been badly injured. His father, Ali, was killed in 1988 by a man about whom the family had warned police.

The court ruled that although in that case the police could not be criticised, if in future they failed to take appropriate measures to avoid risks, the State might be liable for that failure.

Austria says that the extraordinary act of a single criminal should not be regarded as a comment on the state of the nation. Records of Josef Fritzl's previous sex offence were expunged because Austrian law guarantees the right of offenders to be rehabilitated without a spot on their record ten years after serving their sentences.

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