A detective believes Madeleine McCann may have "wandered off" on the night she disappeared.

It’s been 12 years, to the month, since Madeleine McCann vanished.

The McCann family were on a holiday in Portugal, when Kate and Gerry McCann left their three kids in their holiday apartment while they dined at a restaurant just 83 metres away.

When Madeleine’s mother came to check on her three children, one was missing. Their three-year-old daughter, Maddie, had disappeared, and there’s been no credible sighting of her since.

Photos of the wide-eyed little girl have circulated in the media for years, making her one of the most recognisable missing children in the world.

In March this year, Netflix released an eight-part documentary The Disappearance of Madeleine McCann, reigniting discussion and theories about what exactly happened to the little girl on the evening of May 3, 2007.

From a sex-trafficking theory to conjecture that her parents know exactly what happened, it would seem that all possibilities have been considered and explored.

Could Madeleine McCann’s parents have been involved in his disappearance? Post continues after audio…

But what is the likelihood that the three-year-old wandered off?

There has been a line of inquiry that Madeleine McCann woke from her sleep during the night, wandered off looking for her parents, and drowned in the nearby ocean or was hit by a car.

Jim Gamble was the most senior child protection police officer when Madeleine disappeared in 2007, and was involved in the search for the three-year-old initially.

Speaking to Daily Star, he says this theory has some basis.

“What we do know is, Madeleine is missing.

“Either someone took her – could be anyone – or in fact she wandered out that night, came to harm and her body has never been discovered,” he told the publication.

“You’ve got to consider the hypothesis that in fact she was taken.”

According to The Sun, Operation Grange, the name given to the Metropolitan Police’s investigation for the search of Madeleine McCann, have discussed this theory at length with Portuguese police.

"One of the lines of investigation that continues to be pursued is that Maddie could have walked out of the holiday flat herself," a source in Portugal told the publication.

However Kate and Gerry McCann have always refused this theory, with a family source previously saying: "Kate and Gerry have always maintained that their daughter was abducted and simply didn’t get up and wander off to her fate".

"There were heavy shutters which would have been impossible for a small child to open."

As the Netflix documentary explains, the sliding door to the apartment was unlocked and the apartment was close to the road and within walking distance to the beach.

The police investigation into the disappearance of Madeleine McCann is remains ongoing.

For more on this topic:

The 7 most compelling theories about what happened to Madeleine McCann.

After Madeleine McCann disappeared, police offered Kate a deal to confess to her murder.

Madeleine McCann has been missing for 12 years. DNA testing could solve her case in a week.

Madeleine McCann's parents don't want you to look at these images of their daughter.