Spanish private detectives claim they handed Scotland Yard up to eight “very important leads” in the search for Madeleine McCann.
Four Metropolitan Police officers held talks with Barcelona firm Metodo 3, which investigated her disappearance on behalf of the family, sources said.
Officers travelled to Spain on Tuesday to pick up around 30 boxes of documents, investigator Francisco Marco Fernandez told Spanish TV.
Mr Fernandez, who was hired by parents Kate and Gerry for six months, said he provided police “with all the documents and information we have collated worldwide about Madeleine’s disappearance”.
“I think there are six, seven or eight very important leads in there,” he added.
Family spokesman Clarence Mitchell said: “Kate and Gerry will simply not be commenting whilst the Metropolitan Police review of Madeleine’s case is under way.
“They remain pleased that the Met team is continuing its work and that progress is being made.”
It is the second time officers are understood to have visited the Spanish city. A team also spent three days there with Spanish colleagues last month discussing her disappearance in Portugal.
The Metropolitan Police force has said there would be no limits in its re-examination of the search and officers have also travelled to Portugal three times in connection with their review.
Madeleine was nearly four when she went missing from her family’s holiday flat in Praia da Luz in the Algarve on May 3 2007 as her parents dined with friends.
The review was sparked after a request from Home Secretary Theresa May supported by Prime Minister David Cameron.
Portuguese detectives, helped by officers from Leicestershire Police, carried out a massive investigation into Madeleine’s disappearance.
But the official inquiry was formally shelved in July 2008 and since then no police force has been actively looking for the missing child.