Police investigating the disappearance of Madeleine McCann have said they have drawn up a "good number" of potential suspects who may have abducted the schoolgirl.

Metropolitan Police have said they have drawn up a list of names who are "of interest" to the investigation.

The official Portuguese police inquiry into Madeleine's disappearance ended in 2008, but Scotland Yard launched a review into the search following a request by Prime Minister David Cameron from the girl's parents Gerry and Kate.

Madeleine went missing from Praia da Luz in Portugal's Algarve in May 2007 when she was four year's old.

Det chief supt Hamish Campbell said: "The purpose of the review was to look at the case with fresh eyes and there is always real benefit in doing so.

"The review has further identified both investigative and forensic opportunities to support the Portuguese.

"There is more than a handful of people of interest which could be explored further if only to be eliminated.

"The key things are to investigate the case and our work is happening to support the Portuguese."

Clarence Mitchell, spokesman for the Madaleine's parents, said: "Kate and Gerry remain very, very pleased with the work that Scotland Yard are doing and have been encouraged by Operation Grange from the day it began.

"Beyond that, they simply will not comment on what are police operational matters."

Speaking to the Evening Standard on the eve of his retirement from the force, Campbell said: "We have to ask ourselves why are cases unsolved and, on many occasions, we find we passed the suspects by already and the suspect sits within our system."

"The Portuguese hopefully will pursue some of these investigative opportunities with our assistance. There is room for further work and collaboration to resolve the case."

When asked if Madeleine - who would now be 10-years-old - could still be found alive, he replied: "You cannot exclude it."

He added: "You only have to look at the case in Cleveland, Ohio, and the European cases. Of course, there is a possibility she is alive, you cannot exclude it. But the key is to investigate the case and, alive or dead, we should be able to try and discern what happened."

Shortly before the sixth anniversary of her disappearance, Madeline's parents spoke of how they believed the police review into their daughter's disappearance is making "excellent progress".

A Met Police spokesperson said: "Our investigative review is ongoing and we are encouraged by the progress we are making. We are reviewing a significant number of documents and continue to identify potential lines of inquiry.

"We can confirm that as part of this process we have identified a number of persons of interest, but any suggestion that the MPS is asking the Portuguese Police to make arrests in connection with this inquiry is entirely inaccurate.

"We are in regular contact with Kate and Gerry McCann and they are kept fully updated on the progress of our work.

"We also continue to work closely with the Portuguese Police and are actively considering our next steps."