Met Police want to speak to a number of men about a large number phone calls they made in the area on the night the child vanished.
The Portuguese inquiry into the disappearance of Madeleine McCann has been reopened amid new leads in the case.
Six years on from her disappearance, Portuguese police are set to re-open the case into missing Leicestershire girl Madeleine McCann.
Officers have said that they will travel regularly to Portugal as part of the UK investigation, following a meeting with Portuguese police, the Met Police said in a statement.
Assistance Commander Mark Rowley, specialist crime and operations, said: "The meeting was very positive, and we and the Policia Judiciara have a shared determination to do everything possible to discover what happened to Madeleine.
"Colleagues in Portugal fully shared with us the developments in their review, and the fact that they were taking the significant step of applying for the investigation to be formally reopened.
"From the near future, MPS detectives from Operation Grange will travel regularly to Portugal under the terms of the ILOR in relation to the UK investigation."
This is a very significant development in the search for Madeleine, for an investigation to be re-opened there has to be a substantial amount of new evidence and it is clear that the Attorney General feels that the review which has been going on in Portugal has generated that information.
This is also completely separate from the investigation by the British police, so it is quite significant that we have two investigations both finding new things that need to be looked at.
We understand that already police officers from this Portuguese review are on the Algarve, starting to work out a plan of action, who they wish to speak to, what questions they want to put to them.
Amongst that group we think there are a number of men who were though to be in the area at the time who have been on various sex offenders registers both in Portugal and abroad.
What is important about this is it seems to suggest they are moving towards the thought that Madeleine may have been taken by a foreign group of paedophiles.
The investigation team who have been working on this are all specialists in child abduction. Child abduction is not something the Portuguese were absolutely sure had taken place in the early days of this investigation, so it is quite telling that they have shifted their focus that way.
Madeleine McCann's parents Kate and Gerry said today they are "very pleased" that Portuguese authorities plan to re-open their investigation into her disappearance.
They have said they hope that it will uncover "the answers we so desperately need".
According to the Metropolitan Police, who will be working with the Portuguese investigators on the case, "new lines of enquiry" have opened up which warranted the investigation being re-opened.
Portuguese investigation will run in parallel with Met's Operation Grange #McCann
AC Rowley: "This is a welcome development but both investigations at relatively early stages, with much work remaining to be done" #McCann
The Portuguese attorney general has said new leads mean the formal investigation into Madeleine McCann's disappearance needs to be reopened.
The Home Secretary said she welcomed the news that Portuguese police would re-open the case in to the disappearance of Madeleine McCann.
Theresa May said: "I welcome the developments that have taken place and the work the Metropolitan Police are doing with the Portuguese police on this case. I hope that what we're going to see is a resolution to this case for the sake of Maddie's parents and family."
The parents of Madeleine McCann believe it would be an "important step forward" if Portuguese police reopened the investigation into the disappearance of their daughter.
A spokesman for the couple told the Daily Mirror: “Kate and Gerry don’t want to get their hopes up too much. But if the Portuguese do resume their investigation it would be a significant development and an important step forward.”