To mark the occasion her parents Kate and Gerry gave a moving interview in which they said they would do "whatever it takes for as long as it takes" to find their daughter.
A source told the Sunday Express: "Detectives have scoured Europe looking for this woman who is thought to hold the key to solving the entire case.
"After months of tireless police work they will soon be in a position to move in and finally get some answers after a decade of dead ends. It is a hugely significant line of inquiry that officers hope could lead to an arrest."
Scotland Yard's Assistant Commissioner, Mark Rowley, last week said his team would never give up hope of finding out what happened to Madeleine, who was three when she went missing.
He said there remained a number of critical lines of inquiry including one lead which "could provide an answer" as four detectives remained dedicated to the case.
The initial Portuguese police investigation was closed in 2009, but in 2011 the British government provided the Metropolitan Police with funding to review the case.
A Metropolitan Police spokesman said that they could not discuss details of any ongoing investigation.
As part of their six-year-long review of the case British officers have examined more than 40,000 documents and investigated around 600 people of interest.
In 2013 four potential suspects were identified and interviewed by police in Portugal, but they were all subsequently eliminated from enquiries.
This story was originally published by The Daily Telegraph.
