According to an email sent by the Metropolitan Police a child abduction ring based in Belgium placed an order for a “young girl”.

Three-year-old Madeleine was spotted while on holiday in Portugal by someone connected to the gang who took a picture of her.

The photograph was sent back to Belgium where the paedophile ring agreed that she should be abducted, the email states.

Three days later on May 3rd last year Madeleine was taken from her family’s holiday apartment in Praia da Luz in the Algarve while her parents ate at a nearby restaurant.

The astonishing revelation supports Kate and Gerry McCann’s long-held theory that their eldest child may have been taken by a child smuggling ring.

The email, sent by an intelligence officer on the Met’s vice squad on March 4 this year to counterparts in the Portuguese and Leicestershire police, marks a significant development in the case of the missing girl.

Just last month Portuguese police closed their investigation and cleared the McCanns of any involvement in their daughter’s disappearance.

The email was revealed for the first time in police files made public this week.

The Met Police were tipped by an anonymous source, the files showed.

Met officer John Shord wrote the email to Leicestershire Police on March 4 which was passed on to Operation Task – the British end of the investigation into Madeleine McCann.

It said: “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.”

DC John Hughes, from Leicestershire Police, forwarded the email to the Policia Judiciaria (PJ) at Portimao in the Algarve on April 21, the files showed.

The next day the email was sent to Ricardo Paiva, one of the three Portuguese police officers leading the investigation.

On April 28, Portuguese police faxed the information to Interpol in Lisbon and asked them to investigate it as a matter of urgency.

Interpol replied on May 23, passing on all information gathered from its bureaus in London, Brussels, Germay and Finland.

On May 27, Interpol in Lisbon sent an urgent fax to Portuguese police asking for more information, but an undated return fax told them they had all the information that there was.

The email emerged in volume 14, appendix five, of the vast Portuguese police dossier into the closed investigation which was released to the public on Monday.

Paulo Rebelo, the head of the police investigation into Madeleine, ordered that the information be placed in the case file.

The inquiry was then shelved on July 21, less than two months after Interpol was told there was no further information about the paedophile ring.

Belgium has featured in the case already. There was an alleged sighting last August in Tongeren on the Dutch Belgian border but it was later ruled out.

The country was at the centre of one of the most notorious paedophile investigations of recent years which saw Marc Dutroux jailed for life in 2004 after being convicted of kidnapping, raping and murdering young girls.

He was found guilty of kidnapping and raping six girls, killing two of them and causing the deaths of two others. The case surrounding Dutroux, 47, an unemployed electrician and a convicted paedophile, shocked Europe in the mid-1990s.

Mr and Mrs McCann, from Rothley in Leicestershire, have spent the last 15 months trying to find their daughter who disappeared from her family’s apartment in Praia da Luz last May.

For 10 months the couple had to battle to clear their own names of suspicion after they were named as suspects.

Only now, is a picture emerging of what may have happened.

It destroys the PJ’s theory that the couple accidentally killed Madeleine and then tried to dispose of her body.

The couple’s spokesman Clarence Mitchell said: “Their private investigators 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.”

A friend of Mr and Mrs McCann added: “Trafficking into Belgium forms a very strong part of their investigation as does trafficking into north Africa.

“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.”

A Scotland Yard spokesman said: “Unsubstantiated information was received by CO14 relating to the disappearance of Madeleine McCann.

“This was passed on to Leicestershire Police on 4th March 2008. The information was further discussed with Leicestershire Police verbally and all possible lines of enquiry were conducted.

“Leicestershire Police passed the information on to the Portuguese authorities.”