An informant told police in London that Madeleine McCann was stolen to order by an international paedophile ring, according to newly-released documents.
The unnamed source said a spotter took photographs of her while she was on holiday with her family in Portugal and sent them to the group in Belgium.
The ring then ordered her abduction from the Algarve resort of Praia da Luz three days later on May 3, 2007, according to the informant.
Scotland Yard sent the information in an e-mail to their counterparts in Leicestershire, where the McCann family lives. It was then passed to detectives in Portugal.
"Intelligence suggests that a paedophile ring in Belgium made an order for a young girl three days before Madeleine McCann was taken," the e-mail says.
"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."
A Scotland Yard spokesman confirmed that they had passed on the information in an email, but would not comment on the identity of the informant, the reliability of their information or how seriously the claim was taken.
In a statement, the Metropolitan Police said: "Unsubstantiated information was received by CO14 (Scotland Yard's clubs and vice unit) relating to the disappearance of Madeleine McCann. This was passed onto Leicestershire Police on March 4.
"The information was further discussed with Leicestershire Police verbally and all possible lines of enquiry were conducted."
Portuguese police released thousands of files relating to the girl's disappearance, which happened shortly before her fourth birthday, after they said her parents, Kate and Gerry McCann, were no longer suspects.
Portugal's chief prosecutor Fernando Pinto Monteiro said the case was being shelved due to a lack of evidence.
The McCanns have always denied having anything to do with their daughter's disappearance and say they fear she was abducted.
Their spokesman Clarence Mitchell was not immediately available for comment.