Child-porn police draw a blank in hunt for missing Madeleine after trawl of indecent pictures

Portuguese police seized the images in raids on the homes of suspected paedophiles last week.

Madeleine's parents - Gerry and Kate - were said last night to have reacted to the development with mixed emotions.

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"They're torn between huge relief that she's not been found in the clutches of a paedophile ring, and dismay that the investigation has hit yet another brick wall," said a friend.

"They continue to hope and pray that Madeleine will be found safe and well."

The raids, dubbed Operation Predator, were not formally linked to the Madeleine investigation but officers trawled through thousands of pictures and videos in an attempt to find a link to the four-year-old.

Any clues to her whereabouts would have been passed to the detectives leading the search.

Child protection officers found hundreds of images of light-haired children on the seized computers, including some whose faces had been digitally distorted to stop them being recognised.

Detectives used software to unscramble the children's faces but said none closely resembled Madeleine who went missing in the Algarve on May 3.

They are understood to have used advanced technology similar to that employed by Interpol last week in the unmasking of a European paedophile who had posted hundreds of images of himself online.

The offender, codenamed Vico, had protected his identity by digitally altering his face. He was shown sexually abusing boys in Vietnam and Cambodia.

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Interpol received hundreds of calls identifying him when they used an unscrambled picture in a worldwide appeal last week.

Officers probing Madeleine's disappearance had hoped her abductor could be unmasked in a similar way.

They had seized 150 computers belonging to 80 child abuse suspects.

Clarence Mitchell, a spokesman for the McCann family, said: "We are unable to comment on anything that goes to the heart of the investigation.

"However, it does sound as if one avenue of investigation has been closed.

"Kate and Gerry would be pleased to see the police continuing their investigation and want to see Madeleine home safely."

Meanwhile, the results of tests in Birmingham on hair and bodily fluids which are thought to belong to Madeleine have been received by police in Portugal, according to reports.

Officers have told Portugeuse newspapers they expect the results to be "significant". But British sources say the results will not be conclusive.

The McCanns, both doctors aged 39, were waiting to learn the result of the tests carried out on samples taken from their holiday apartment and hire car.

Detectives have insisted that all lines of investigation remain open but continue to assess evidence that the couple, from Rothley in Leicestershire, could have been involved in Madeleine's disappearance.

The new head of the inquiry, Paulo Rebelo, has ordered his officers to review every aspect of the investigation and to carry out fresh searches of the area around Praia da Luz.

Madeleine disappeared from the resort on May 3.

The forensic results are expected to be given to police later this week.

Sir Richard Branson, who gave £100,000 to fund the McCanns' legal team, said yesterday that he had backed them because he felt they had been treated unfairly by Portuguese police.