Detectives investigating the disappearance of Madeleine McCann will today begin interviewing 11 people considered witnesses and suspects in the seven-year mystery.

Police from the British-led investigation Operation Grange will be in attendance, but it is understood Portuguese officers from the Policia Judiciaria will lead the questioning.

Seven of the number are believed to be 'arguidos', which means they are treated as formal suspects but have not been charged with a crime.

In Portuguese law, police can declare a suspect to be an arguido in order to ensure they cannot travel abroad and can be used as a pre-cursor to charging a suspect with an offence.

However, the status also gives the suspect the right to refuse to answer questions and secure legal representation.

A further four people are being interviewed as witnesses to the disappearance of Madeleine who vanished from a holiday apartment in Praia da Luz in May 2007 while her parents Gerry and Kate were dining with friends nearby.

It is believed that one of the men police will question as a witness is Robert Murat, who was declared an arguido by Portuguese police in the initial investigation.

He was later cleared and won substantial libel payouts from several media organisations. Mr Murat says he is happy to help the investigation and has nothing to hide.

It is believed the interviews will be attended by detective chief inspector Nicola Wall, who will officially take over control of Operation Grange on December 22nd after the departure of detective chief inspector Andy Redwood.

Earlier this year, Scotland Yard detectives returned to Portugal to help interview several people over the case.

It followed on from searches of three areas of land near the Ocean Club, the hotel where the McCanns were staying.

Portuguese and British investigators excavated an area of scrubland to the west of the resort at the start of June but found no evidence related to the case.

Portuguese police closed their investigation in 2008, but the Metropolitan Police launched its own inquiry three years later.