If Madeleine McCann was abducted by a paedophile, there is a chance that she is still alive and can be saved by sensitive policing, according to Ray Wyre, a sexual crimes consultant.

“Lately, there have been more and more cases where there has been an element of planning and an attempt to keep the child alive,” he said.

The most notorious such case involved the Belgian paedophile Marc Dutroux who kidnapped a 12-year-old girl in 1996 and kept her in a cellar for 80 days, a victim of abuse.

In Britain, Alan Hopkinson, a convicted paedophile, kidnapped two 10-year-old girls in 1999 and held them in his flat in Eastbourne for three days, subjecting them to assaults. They were rescued by police.

To maximise the possibility of finding Madeleine alive, police must avoid doing anything to make the kidnapper panic. If he believes that they are about to move in and catch him, he may become so alarmed that he kills the child to stop her being a witness.

Dutroux was jailed on his victim’s testimony.

Sometimes children are kidnapped by barren or bereaved women or couples desperate to become parents. “That would offer great hope because the child would be looked after,” Mr Wyre said.

But the way Madeleine disappeared suggests a more sinister purpose. Her younger twin brother and sister were left in cots beside her. Yet a baby would have been much easier to snatch and hide.

Mr Wyre has worked closely with the notorious serial sex killer Robert Black, who murdered at least three girls by snatching them into his van. He is suspected of killing a dozen children around Britain.

The expert said that paedophiles were attracted by perfect-looking children like blonde Madeleine. If sex was the motive, she may have been chosen for her appearance. Children abducted by paedophiles have often been killed a few hours later or, at most, within the day. A child stolen for sex is often dead before anyone even reports they have gone.

Portugal is known to attract British paedophiles. A ring of 20 Britons set up there around 1990, filming sex acts with local boys and sending the tapes to Belgium and the Netherlands. Some were later jailed in England. The case helped to persuade the British Government to make it illegal for Britons to have sex with underage children abroad.

Mr Wyre went to Lisbon and became involved in the aftermath of that investigation. “There were still lots of connections and other things going on,” he said. “There have always been British paedophiles operating in Portugal.”

Although Madeleine’s parents will be feeling guilty for leaving her, Mr Wyre said that nothing can stop a determined paedophile except his capture.

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