Raymond Hewlett was staying near Praia da Luz, in Portugal, when the three-year-old went missing in May 2007, according to reports.

Police from Yorkshire are preparing to fly to Germany to question the convicted paedophile who is being investigated over the disappearance of Madeleine.

Former soldier Raymond Hewlett, who has been jailed for sex attacks on young girls in Calderdale, is said to have been staying near the McCanns' holiday flat in Portugal when Madeleine went missing in May 2007.

He is undergoing treatment for throat cancer in a German hospital, but police want to interview him about an indecent assault which occurred in West Yorkshire 34 years ago.

Detectives in West Yorkshire are understood to have been monitoring Hewlett's movements in Europe for "some time" and have asked German authorities for permission to question him.

A West Yorkshire Police spokeswoman said: "We wish to interview Hewlett in connection with an indecent assault which occurred in 1975.

"We are unable to provide any more details about the incident because it is an ongoing investigation.

"We have made contact with the German authorities. We are just waiting for clearance so we can actually go and speak to him regarding that incident."

Hewlett has been jailed several times for sexual offences against young girls and was investigated over the killing of Lesley Molseed.

She was sexually assaulted, stabbed 12 times and her body dumped on moors above Ripponden.

In September 1972 he abducted a 12-year-old girl and took her on to moors near his home in Todmorden.

He incapacitated her with a rag soaked in paint thinners and she only escaped being raped after he ejaculated prematurely.

In 1978 Hewlett attacked another girl, this time putting a gun to her back but she managed to convince him visitors were arriving imminently and he let her go.

Hewlett, a former soldier, was one of seven men featured in a News of the World campaign which urged the public to be on the lookout for missing paedophiles.

He also appeared on a Crimestoppers list of Most Wanted paedophiles.

A source close to the Madeleine McCann investigation said Hewlett is wanted for questioning by police forces in Greater Manchester, West Yorkshire, and Leicestershire, as well as by the Irish police.

The 64-year-old is reportedly being treated for throat cancer in a German hospital.

Clarence Mitchell, spokesman for Madeleine's parents Kate and Gerry, said Hewlett was a line of inquiry being looked at by investigators working for the Leicestershire couple.

Mr Mitchell said: "We are aware of Raymond Hewlett, and the claims that have been made about him in some newspapers."

The alarm was raised about Hewlett by a couple who met him while on holiday in Portugal, the Daily Mirror said today.

Alan and Cindy Thompson said Hewlett was living with his wife and six children in a converted Dodge truck travelling from campsite to campsite.

Mr Thompson, 56, told the newspaper: "Hewlett befriended us but kept quiet about his terrible past.

"We were mortified and disgusted to discover the truth."

They described a conversation in which Hewlett said he was approached by some "Gipsy tourists" offering to buy his daughter just before Madeleine went missing.

Mrs Thompson, 47, said: "We didn't think too much of this at the time. Ray and his family led a desperate hand-to-mouth lifestyle and someone may have thought he'd be tempted to sell one of his six children."

They also recalled him mentioning a "business" trip to Morocco, where there were several alleged sightings of Madeleine in the months after her disappearance.

Earlier this week, the Thompsons contacted Hewlett to question him about his movements, the Mirror said.

Hewlett told the Thompsons he had done nothing wrong and they were judging him based on what they knew of his past, the paper reported.

He said: "If you've chosen to believe anything I can't do anything about it anyway, so there you go. Catch 22.

"You're basing it on someone's past, rather. That means the person's past is important. Doesn't make him guilty. You shouldn't be talking to me about it. I've done nothing wrong, nothing, nothing.

"I don't actually believe that child was actually kidnapped, let alone murdered."