LONDON — Investigators with Britain’s largest police force said on Wednesday that they believe that Madeleine McCann, the British toddler who vanished while on vacation with her parents in Portugal, could still be alive. Madeline’s tragic story reverberated across the globe, and as the years have passed most have given up hope of ever finding her.


But a week before the anniversary of her disappearance, the Metropolitan Police released a statement saying its investigators had uncovered what they believed to be “genuinely new material,” as well as nearly 200 new opportunities for further inspection. Investigators said that they “now believe that there is a possibility Madeleine is still alive,” and have called for the investigation by Portuguese police to be reopened after an almost four-year hiatus.


Along with the statement, the Metropolitan Police, commonly known as the Met or Scotland Yard, released an age-progression image ahead of what would have been Madeleine’s ninth birthday on May 12. The haunting image of a wide-eyed 3-year-old, relayed worldwide in the weeks after her disappearance on May 3, 2007, has been replaced by that of a 9-year-old with her blond hair swept in a side-part, created in collaboration with her family.


While the initial investigation by the Portuguese authorities was roundly criticized, the British inquiry has been aided by the fact that, for the first time since Madeleine disappeared from her bedroom in the family’s rented apartment in the Algarve region of Portugal, investigators have been able to review material generated by three independent investigations in one location.


The detective leading the review said that having access to the Portuguese investigation, inquiries by British law enforcement agencies and the work of private investigators hired by the McCann family presents the team with “best opportunity” of finally solving the mystery of what happened in the seaside resort of Praia da Luz.


Officers have so far identified 195 new items for investigation within the historic material, as well as having developed the new material. A Metropolitan Police spokesman appealed to “anyone who is able to provide direct information as to her whereabouts” to contact the authorities.


Madeleine was just nine days shy of her fourth birthday when she was abducted as she was sleeping along with her younger twin siblings while her parents, Kate and Gerry McCann, dined with friends in a tapas bar 100 yards away.


Rewards totaling millions of dollars were offered by wealthy Britons, including J. K. Rowling, the billionaire author of the Harry Potter series, and Richard Branson, the airline tycoon. But the Portuguese police identified only one suspect, a 33-year-old Britain living with his mother in a nearby apartment. They also scrutinized the parents at one point, though it seemed unlikely to most investigators that they would harm their own child, particularly as the twins went untouched.


Despite the publicity created by an international campaign and continued claims of sightings (the latest of which came on the Costa del Sol in Spain last week), the official investigation by the Portuguese police was formally closed in July 2008. At the time, even Portuguese prosecutors faulted the country’s police for failing to uncover any clues in the girl’s disappearance.


In May last year, however, a separate Metropolitan Police inquiry, codenamed Operation Grange, was established after Prime Minister David Cameron responded to a plea from Madeleine’s parents. The objective has been to present to the Portuguese authorities fresh avenues of investigation, with a view to having the case reopened.


The task force, led by Detective Chief Inspector Andy Redwood, consists of 28 detectives from the Homicide and Serious Crime Command and seven civilian staff members who have been working in “close collaboration” with a senior investigating officer from the Portuguese police.


While officers have made two trips to Spain and visited Portugal four times, most recently last week, the thrust of the investigation has been a methodical analysis of more than 40,000 pieces of information already collected.