The victims of a network of doctors and nurses who allegedly stole babies in Spanish hospitals and sold them for adoption today called on the country's attorney general to open an investigation.

The families of 261 babies who disappeared in Spanish hospitals over five decades presented their case to the attorney general's office in Madrid, including evidence from nurses and people who admitted illegally adopting babies.

What started as a system for taking children away from families deemed to be politically dangerous to the regime of General Francisco Franco became an illicit business that continued into the 1980s or later, a campaign group has claimed.

Doctors, nurses, nuns and priests are all suspected of forming part of an organised network that told mothers their children had died during, or straight after, birth. Campaigners said they believed many thousands of cases of stolen babies would eventually come to light.

"The father of a friend of mine admitted to him that both he and I had been bought from a priest and a nun from Zaragoza after being born in the Miguel Servet hospital," Antonio Barroso, who discovered four years ago that he was adopted, said.

DNA tests have proved that the people who raised him were not his real parents.

Enrique Vila, a lawyer who represents the National Association of Irregular Adoptions, said: "There are cases that are accompanied by proof in the form of DNA tests and others that are simply mothers who suspect that their babies were stolen.

"We think it was an organised mafia which continued to operate even after the Francoist laws allowing the children of Republican mothers to be given away had been changed."

Inés Pérez, 89, has confirmed that a priest and a doctor in Madrid encouraged her to fake a pregnancy so she could be given a child due to be born at the city's San Román clinic in 1969. Her adopted daughter, also called Inés, is among those wanting the attorney general to investigate.

A nurse from the same clinic has confirmed that babies born there were illegally given into adoption.

In a separate case, workers from an undertaker's in Malaga, in the south, said they sometimes buried empty children's coffins that arrived from a local hospital.

The street outside the attorney general's office was full of people today, many of them weeping, who hoped to discover what had become of their lost children.

Many said they were told that apparently healthy babies had died within hours of birth. They had never seen the bodies and the hospitals had taken care of the burials.

In many cases, the records have disappeared, either because of administrative chaos in hospitals or because they were deliberately destroyed.