The Met expressed the hope that Maddy - who would be now approaching her ninth birthday - was still alive and called for the Portuguese investigation into her disappearance to be reopened.
That investigation was closed in 2008 after 15 months, and authorities said it would be reopened only with new evidence from a "serious, pertinent and authoritative" source.
Yesterday, Detective Chief Inspector Andy Redwood said: "We genuinely believe there's a possibility that she's alive." But he added that his "open-minded" investigation was also looking into the possibility that Madeleine was dead.
His call to reopen the inquiry was based on the findings of a team of 37 detectives and staff who for nearly a year have been working their way through the "vast" amount of material gathered by British and Portuguese police who investigated the disappearance.
Madeleine was nearly 4 years old when she vanished while sleeping with her two siblings in the family's holiday apartment in the Algarve resort town of Praia da Luz.
Last year, the Home Office asked Scotland Yard to conduct a review of the case after the McCann family complained the Government had not done enough and appealed to Prime Minister David Cameron to intervene.
The review team brought together the documentation from inquiries by police from both countries. The vast cache of documents is being filed on a computer system along with the findings of private detectives brought in by the McCanns to help with the search.
The system analyses the information and can find links where none had been spotted before.
Detectives said yesterday that they had worked through about a quarter of the 100,000 documents, and other material, which had thrown up 195 "investigative opportunities".
It's understood that while none is a "golden nugget", some are significant and have contributed to the theory that Madeleine, who would turn 9 on May 12, is still alive.
The trawl has also highlighted gaps in the original investigation, and Redwood appealed for anyone who may have been at the resort at the time of the disappearance to come forward to help plug these.
While yesterday's developments brought some hope for Madeleine's parents, Kate and Gerry McCann, the case has taken its toll. They have put in upwards of £3 million (nearly $6 million) from public donations, libel settlements - when their own role in her disappearance was questioned - and from the proceeds of a book by Kate McCann into solving the mystery.
"Kate and Gerry have always been firmly of the belief that she is alive," said their spokesman, Clarence Mitchell. "There's absolutely no evidence to the contrary."
THE LONG CHASE
May 3, 2007: Madeleine McCann goes missing from Praia da Luz, Portugal.
May 15, 2007: Briton Robert Murat is questioned by police.
August 31, 2007: The McCanns take libel action against a Portuguese newspaper's claim police believe they killed their daughter with an accidental overdose of sedatives.
October 2, 2007: A senior policeman is removed from the inquiry after accusing the McCanns of manipulating the British police.
March 18, 2008: The Daily Express and Daily Star pay damages to the McCanns over stories hinting at their involvement in the disappearance.
July 21, 2008: The Portuguese police shelve their inquiry after 15 months. The McCanns and Murat are cleared of any blame.
May 12, 2011: The Home Office says it will ask Scotland Yard to help search for Madeleine.
Yesterday: Scotland Yard reveals its has identified nearly 200 new possible leads.
- Independent
