Detectives investigating the disappearance of Madeleine McCann say they are set for a "substantial phase of operational activity" in Portugal in the coming weeks.
Assistant Commissioner Mark Rowley, of Scotland Yard, said: "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."
Mr Rowley also echoed Kate McCann view that media intrusion does not aid the police investigation.
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.