Detectives investigating the disappearance of Madeleine McCann are set to stage "a substantial phase of operational activity" in Portugal in the next few weeks.
Assistant commissioner Mark Rowley from Scotland Yard said that officers are working through every credible line of inquiry in the search for the missing three-year-old, as part of the "slog of a major investigation".
He said: "In the forthcoming weeks we are going to be going to a substantial phase of operational activity on the ground in Portugal."
The senior officer stressed: "It's something that you would expect in any major inquiry.
"A thorough serious crime investigation works systematically through all the credible possibilities, and often in an investigation you will have more than one credible possibility.
"Therefore just because we're doing a substantial phase of work in the forthcoming week doesn't mean that it's going to immediately lead to answers that will explain everything."
British police are currently running their own investigation into what happened to Madeleine, who vanished from Portuguese holiday resort Praia da Luz in May 2007.
The Portuguese have now also re-opened their inquiry into her disappearance, and while they are working with the UK force have refused to set up an official joint investigation.
Mr Rowley echoed Kate McCann's calls for restraint in media coverage of the case, and said: "I want to be able to go back to Kate and Gerry at some stage in the future and tell them we've got to the bottom of this, or second best is to go back to them and say we've turned over every stone and we can't get to an answer sometimes."
A number of officers from Scotland Yard are hoping to be involved in the latest phase of activity.
"The activity in Portugal is led by the Portuguese, that's absolutely crystal clear in law," Mr Rowley said.
"We have some officers who would like to be helping with that on the ground in Portugal, doing some of the work we anticipate. We are putting the finishing touches to the plans to the Portuguese in the coming weeks."
He added: "I anticipate a substantial phase of activity in forthcoming weeks including Portuguese and British officers but the detail of that is still being finalised with Portuguese colleagues and it will all be under Portuguese leadership."