German police plan to head back to Portugal after receiving a new tip by British tourists over the disappearance of Madeleine McCann - but they may be blocked.
Police hope to return to the resort and apartment in Praia Da Luz where McCann vanished in 2007 to follow up new leads.
The German authorities believe boots on the ground in Portugal could help give them enough evidence to charge prime suspect and paedophile Christian Brueckner.
"German officers think getting their team's boots on the ground would be a massive boost to the investigation," a source told The Sun.
"German detectives have received a lot of excellent information in the past few weeks, especially from British holidaymakers who were in Praia da Luz at the time of Madeleine's disappearance.
"There are leads, tips and lines of inquiry from those witnesses that urgently needed to be followed up."
German police's plans to head to the resort won't go down well with Portuguese cops, who have a frayed relationship with each other.
Portuguese police, whose probe into McCann's disappearance was criticised, ruled out Brueckner as a suspect soon after the 3-year-old disappeared.
The source told the Sun it would be "deeply embarrassing" for Portuguese police if Brueckner was found to be responsible for McCann's disappearance, and may block the Germans from investigating on the ground.
The person said in an ideal situation police in both countries would be working together, but Portuguese police genuinely believe Brueckner didn't do it.
"They think a lot of what is being said by the German detectives is hot air and distracting from the most important thing - finding the person who took Maddie which is something, like the rest of the world, they've always wanted to see."
The latest tip off comes after prosecutors admitted they feared charging Brueckner because of Germany's strict double-jeopardy laws.
For more than a year, prosecutors have been working closely at gathering enough evidence to charge Brueckner with the murder of the 3-year-old back in 2007.
But lead prosecutor Hans Wolters told the Mirror they have one shot at nailing Brueckner, saying if they fall short he will never again be able to be charged for crimes related to McCann.
"If we file charges and he is acquitted, then the case is dead forever," he told the Mirror.
"In Germany, once you have been acquitted, you cannot be charged again, at least only in very exceptional cases.
"If we now are hasty and he was acquitted because the court said 'Ah, we still have a few doubts' then we would not be able to get him later."
Brueckner was in Praia Da Luz at the time McCann disappeared, with cell phone records linking the paedophile to the area within an hour of the child going missing.