Former detective inspector Dave Edgar, hired by the McCann family to lead the investigation into the hunt for Madeleine McCann

The Ulster detective leading the search for Madeleine McCann today reveals his most chilling theories yet, exclusively to Sunday Life. Hardened ex-RUC cop Dave Edgar told us he is convinced that little Maddie is imprisoned in a hellish lair – just like kidnapped sex slave Jaycee Lee Dugard.

He insisted the “back from the dead” reappearance of Jaycee – and the cases of Austrian cellar girls Elisabeth Fritzl and Natascha Kampusch – confirmed his suspicion.

And despite fresh leads taking his probe to Australia and Barcelona, the east Belfast man insists the golden-haired youngster is being held just 10 miles from where she was snatched in Praia da Luz two years ago.

But he warned that the sprawling wilderness where he believes Maddie is languishing is almost impossible to search completely.

Belfast-born Dave revealed the grim theories when he opened his case files to us.

We spent the day at the Cheshire office he uses to conduct the world’s biggest missing person case.

Sunday Life can now lift the lid on how his Alpha Investigations Group private eye agency really operates and what it is like to search for the world’s most famous missing youngster, who disappeared two years, four months and 10 days ago.

When we visited Dave’s headquarters, US kidnap victim Jaycee Lee Dugard had still not been rescued and the world had long forgotten her name.

But even then Dave said he was convinced Maddie was entombed by an abductor in a cellar or dungeon, like Austrian cellar victims Natascha Kampusch and Elisabeth Fritzl.

“Maddie is most likely being held captive, possibly in an underground cellar, just like Natascha or Elisabeth, and could emerge at any time,” he told us.

Days later, news broke that tormented Jaycee had been freed from the foul compound where she was abused for 18 years by monster Phillip Garrido. Dave simply said: “This just supports my theory that Maddie is alive and imprisoned.”

There was further backing for his theory when American boy Ricky Chekevdia was found hiding with his mother in a tiny “secret room” two years after he was kidnapped while caught in a custody battle.

Former detective inspector Dave, who grew up on Belfast’s Woodstock Road, was drafted in by Kate and Gerry McCann last November after Spanish investigators failed to find new leads.

Renowned for leaving no stone unturned in his UK murder investigations, Dave now spends his days with a four-strong team probing every lead that comes in to his office.

His partner Arthur Cowley has more than 30 years’ policing experience in north-west England – and the pair are backed up by a translator and an ex-police administrator.

They have sifted through thousands of emails, answerphone messages and letters to get that one breakthrough lead.

Last month, the information took Dave’s probe to Australia and Barcelona to track a ‘Victoria Beckham lookalike’ suspect, who spoke with an Australian or New Zealand accent.

She was seen asking two British tourists at a marina in Barcelona if they were there to deliver her “new daughter” – three days after Maddie disappeared.

But he told us he is now back to focusing on his original theory.

He still feels Maddie was snatched by a man spotted by the McCanns’ friend Jane Tanner, one of the so-called ‘Tapas Seven’ who dined with them the night Maddie went missing.

Dave said: “Jane is a very reliable witness and there were other sightings of this man, who Jane saw carrying a little girl in a blanket, in the days leading up to the disappearance.”

He feels this is the lone prowler who has Maddie stashed in a cellar or dungeon in the lawless villages around Praia da Luz.

But Dave warned: “This rural, sprawling terrain makes it extremely difficult to search. You could quite easily keep a child there for years and no-one else would know.

“The person who has Maddie is most likely a paedophile or a person so desperate for a family they were willing to kidnap for it.

“I wouldn’t like to speculate on what is happening to her.”

Dave says the region where he feels Maddie is being held has attracted many strange characters, including convicted sex offenders.

“I don’t want to generalise or make gross exaggerations, but there are people there living on the edges of society,” Dave said.

He added there were as many as nine child sex attacks in the area round Praia da Luz from 2005 to 2007 and the victims included British kids.

Some happened as close as 20 miles from Praia da Luz, and six of them were on girls between the ages of three and 10.

He is now investigating leads on six child sex offenders, 78 other rapists and sex attackers and 22 vagrants.

In a glimmer of hope, Dave said: “The key thing is no body has been found.

“When paedophiles kill, they often dump the body nearby, and this isn’t the case here.

“Even if Maddie had been dumped in the sea nearby the resort, the ocean often gives up his victims.

“Until I find evidence that she is dead, I will keep going.” And his plans for the future?

“I don’t know. We could still be sitting here in 10 years.

“If Maddie is being held, she may be being brought up to speak a different language and not even remember her own name or where she was from.

“All we can do is try and keep public awareness high – and try and reach as much of that mountainous region outside the resort as we can.”