Is Madeleine McCann, who'd now be 15, alive and living in Portugal?

A former British police officer says missing Madeleine McCann could be living in Portugal with her captors, completely unaware anyone is looking for her.

A photo of Madeleine McCann. Source: Supplied

The stunning revelation was made by the former top detective who worked for Madeleine's parents Kate and Gerry in a futile search to find their missing girl.

David Edgar, a retired Met detective, told Britain's The Sun newspaper it was highly likely Madeleine was still in Portugal, "with every possibility that Madeleine is still alive".

"She could literally be anywhere in the world but my hunch is that she is in Portugal," Mr Edgar told The Sun.

"The chance that she may have been smuggled out of the country without being detected is highly unlikely. There is someone in Portugal with an open knowledge of where she is and what happened."

He continued: "There is every possibility that Madeleine is still alive and could be being hidden somewhere and having no idea that she is at the centre of a worldwide hunt for her."

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He said Madeleine, who would now be 15, was likely taken by a paedophile gang as a three-year-old from a holiday apartment in Praia da Luz in 2007.

"The best hope of a breakthrough, even after all this time, will be if and when someone's conscience is pricked. It may be that the person responsible for Madeleine's kidnap is dying and makes a deathbed confession, or someone close to that person comes forward after he or she has passed away.

Madeleine McCann. Source: BBC

"Or it could be that the abductor falls out with others who know and they finally decide to contact police.

"Whoever is responsible will have confided in someone else. They usually do and it is very rare that they don't."