Police investigating the disappearance of Madeleine McCann in Portugal have cordoned off an area of scrubland amid mounting speculation that they are about to start a digging operation.

The area, in Praia da Luz on the Algarve where three-year-old Madeleine disappeared in May 2007, was taped off and local police officers were seen milling about with dogs.

Scotland Yard, which is carrying out its own investigation into what happened to Madeleine, said the force was "not prepared to give a running commentary" about the case.

The apparent development came two weeks after Assistant Commissioner Mark Rowley from Scotland Yard said officers are working through every credible line of inquiry in the search for the missing girl.

He said: "In the forthcoming weeks we are going to be going to a substantial phase of operational activity on the ground in Portugal.

"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."

The Portuguese have also re-opened their inquiry into Madeleince's disappearance and while they are working with the UK force, they have refused to set up an official joint investigation.

The area cordoned off today has been searched before.

One line of inquiry for Scotland Yard is a lone male paedophile who staged a series of sex attacks on young British girls while they were on holiday in the Algarve.

They are looking at nine sexual assaults and three "near misses" on British girls aged six to 12 between 2004 and 2006, including one in 2005 on a 10-year-old girl in Praia da Luz, where Madeleine vanished two years later.

Hundreds of people have already made contact with police in response to appeals for help to find the attacker.