Gordon Brown today attacked authorities for failing to spot a harrowing trail of incest in the case of the British man jailed for raping his two daughters and fathering nine of his own grandchildren.

Speaking as a major investigation was launched into the failings of police and social services in two counties, the British Prime Minister said the country was "utterly appalled" by the affair and rightly wanted answers.

The 56-year-old businessman from Sheffield held his daughters virtual prisoners for 25 years, moving them around houses in South Yorkshire and Lincolnshire to avoid detection. He received 25 life sentences for rape at Sheffield Crown Court earlier this week, with a minimum term of 19 and a half years.

The details of the case have come to light a fortnight after news of the death of Baby P in Haringey, north London, sparked public outcry and fears that the entire child protection system is fundamentally flawed.

Mr Brown promised any necessary changes would be made to systems designed to save children from abuse, telling MPs: “People will rightly want to know how such abuse could go on for so long without the authorities and the wider public services discovering it and taking action.

“And if there is a change to be made in the system and the system has failed, we will change the system as a result of the inquiries."

The sexual abuse, which has chilling parallels to the case of the Austrian rapist Josef Fritzl, started when the girls were eight years old. Their father would rape them up to three times a week and punch, kick and hold them to the flames of a gas fire if they refused his demands.

The women were at Sheffield Crown Court to hear their father's sentence handed down. The man, who cannot be named to protect his victims’ identities, refused to attend.

The two women became pregnant 19 times in all. Two of their nine children died at birth.

Sentencing Mr X, Judge Alan Goldsack, QC, said: “In nearly 40 years of dealing with criminal cases and 14 as a family judge the combination of aggravating circumstances here is the worst I have come across.”

Politicians and child protection experts asked how the abuse was not detected by the numerous social workers, doctors, teachers and police officers who came into contact with the ever-expanding family over 20 years. Sheffield City Council has launched an independent inquiry, and the role of South Yorkshire Police, Lincolnshire County Council and Lincolnshire Police will also be examined. Both councils said that the family was known to them. The court was told of several contacts with authorities that could have raised the alarm.

Jayne Ludlam, the director of children’s and young people’s services at Sheffield city council in South Yorkshire, said social workers only became aware of the“harrowing” abuse in June this year.

The daughters described their father’s sentencing as a final escape from decades of mental and physical torture. “His detention in prison brings us only the knowledge that he cannot physically touch us again,” they said in a statement. “The suffering he has caused will continue for many years and we must now concentrate our thoughts on finding the strength to rebuild our lives.”

The inquiries are likely to focus on health professionals’ failure to raise the alarm. James Baird, representing the defendant, said that it was inconceivable that the crimes could go un-noticed. “All the signs were indicative of an incestuous relationship,” he said.

Social services in Lincolnshire had contact with the family when the daughters were young and suspicions were raised about the children’s parentage. In 1997 the women’s brother came forward with “hearsay evidence” of incest. Police investigated the claim, but no further action was taken. The family moved back to South Yorkshire in 2004 and social services again became involved, but the abuse went undetected.

During the trial, it also emerged the desperate sisters called an emergency telephone line designed to allow children to report abuse confidentially.

But when they asked for a guarantee that they would be able to keep their children if they informed the authorities of their father’s identity, they were refused and they ended the call.

Chief Superintendent Simon Torr, of South Yorkshire Police, defended the force from claims that it could have stopped the abuse earlier. “This has been a thorough, robust, timely and professional investigation from the moment that the victims first disclosed the abuse, and Sheffield City Council have fully supported the police in bringing about a successful prosecution,” he said.

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