Scotland Yard and other sources passed on tips about a Belgian pervert gang to Algarve police but they believed they were not credible and ruled them out.

 Police intelligence suggesting Madeleine McCann may have been snatched to order for a Belgian paedophile ring is being urgently investigated by private detectives for the little girl's parents today.

Scotland Yard passed on a report from an informant who said a photograph of the child on holiday in Portugal was taken and passed to a "purchaser'' in Belgium days before she vanished, official case files have revealed.

The information was contained in an email from the Metropolitan Police's CO14 clubs and vice intelligence unit included in a massive dossier of evidence made public this week.

Portuguese police pursued the lead with Interpol, which gathered further reports from Belgium, the UK, Finland and Germany.

Credibility

But detective Paulo Rebelo, head of the Madeleine inquiry, ruled that all but the German intelligence showed "lack of credibility'' and ordered that the Scotland Yard tip-off should be filed.

The Metropolitan Police email read: "Intelligence suggests that a paedophile ring in Belgium made an order for a young girl three days before Madeleine McCann was taken."

"Somebody connected to this group saw Maddie, took a photograph of her and sent it to Belgium, the purchaser agreed that the girl was suitable and Maddie was taken.''

The source of the information was anonymous and it is unclear how reliable it is.

The files show the email was sent to Leicestershire Police on March 4 this year -- but it was apparently not forwarded to Portuguese detectives until April 21.

Belgium has something of a reputation for paedophilia after unemployed electrician Marc Dutroux (47) was jailed for life in 2004 after being convicted of kidnapping, raping and murdering young girls.

A friend of Kate and Gerry McCann, both 40, from Rothley, Leicestershire, said the couple's private detectives were taking the possible involvement of Belgian paedophiles very seriously.

"Trafficking into Belgium forms a very strong part of their investigations, as does trafficking into North Africa,'' the friend said.

"There is definitive hard evidence that this is very much alive and happening, and they have looked into the fact that someone was targeting children and they may well have been stealing to order.''

McCann family spokesman Clarence Mitchell refused to comment on "sensitive'' information found in the Portuguese police case files.

He said: "Clearly any information of that nature Kate and Gerry would hope that the Portuguese police in conjunction with Interpol have acted to the absolute best of their ability in following this up."

"The private investigators, as with all the other sightings and all the other information, will be pursuing this line as an absolute priority to establish if it has been fully investigated and properly ruled out."

"They have got some of the information already from their lawyers and investigators and they are waiting to hear from them what is legitimate, what is promising and what is not."

"They are frustrated by the delays and the mistakes that were made."

"They have learned an awful lot about this kind of thing, and God forbid she has fallen foul of any of these types.''

Sighting

This is not the first time Belgium has cropped up in the search for Madeleine -- police investigated a sighting of a girl who looked like the missing child on the border with Holland last August.

A child therapist spotted a young blonde girl at a service station near the town of Tongeren.

Detectives carried out DNA tests on a bottle of milkshake that the child had been drinking from but the tests were inconclusive and the sighting was later discounted.

The McCanns' private detectives are also intensifying their focus on Amsterdam after it emerged that a second witness had reported seeing Madeleine in the Dutch city.

Hannie Wiechmann (71) called police after seeing a young child she believed to be the missing girl in the second week of May last year.

She told the Dutch newspaper Metro she "just knew'' it was Madeleine because of her eyes and her "unequally-cut fringe'' and dyed hair.

But officers dismissed her concerns -- and when she called British police to report the sighting they failed to take her details, she claimed.

This followed the revelation that in early May last year a shop assistant in Amsterdam spoke to a little girl called "Maddie'' who said she had been taken from her mother while on holiday.

The McCanns' team of private investigators were looking "very seriously'' at the possible Dutch connection to Madeleine's disappearance, Mr Mitchell said.

Dutch police refused to comment on the matter, referring inquiries to the Portuguese authorities.

The police files also revealed yesterday that Mrs McCann begged Portuguese detectives to end her "torture'' by keeping her informed about developments in the investigation into her daughter's disappearance.

Madeleine was nearly four when she vanished from her family's holiday flat in the Algarve resort of Praia da Luz on May 3 last year.

Evidence

On July 21 Portuguese prosecutors announced they were shelving the case, although it can be reopened if credible new evidence comes to light.

At the same time the McCanns and Algarve resident Robert Murat were told they were no longer "arguidos'', or formal suspects, in the investigation.

- Sam Marsden