Portuguese police have drawn up a list of 100 questions they want to put to the Kate and Gerry McCann and their circle of friends in a bid to discover the truth about what happened to Madeleine.

Detectives have asked to re-interview the so-called Tapas Nine, the name given to the McCanns and the seven friends who dined with them on the night of their daughter’s disappearance at their Algarve holiday complex.

They also want to talk to relatives, friends, and colleagues of Mr and Mrs McCann, both 39, to gather background information about the couple.

The exhaustive list of queries has been compiled as part of an appeal by the Policia Judiciaria to continue investigating the parents of the missing four-year old.

They want to ask their British counterparts to carry out the interviews on their behalf and are considering a list of 25 character witnesses provided by the McCanns themselves.

"The letter of appeal is concluded," said a police source. “It contains 100 questions, which will be put to Kate and Gerry, their family members, and their friends."

But the public prosecutor in charge of the case in Portugal has refused to sanction further moves against the couple, who were made arguidos - formal suspects - on September 7, without better evidence to back up claims that they were involved in their daughter’s disappearance.

The development came as investigators admitted they had reached an impasse and could not move forward with the case.

"Unless a body turns up or somebody comes forward with a credible lead we do not have the elements to close the case," said a senior police source.

Since taking over as the new head of the investigation in early October, Paulo Rebelo, 45, Portugal’s second most senior policeman, has been methodically reviewing every step of the six-month investigation.

But yesterday it was reported that his efforts have failed to uncover any new lines of inquiry.

"New analysis of the evidence has only confirmed suspicions that exist but nothing more," the police source told Portuguese daily newspaper 24 Horas. "There is no new data despite new operations being carried out in field," he said. Portuguese police are said to frustrated at the delay in receiving the results of forensic tests being carried out in a laboratory in Birmingham,

"The tests were requested over three months ago but the results have not yet arrived. These tests are fundamental to direct or even give a new direction to the investigation," said the same source.

The McCanns' official spokesman Clarence Mitchell yesterday said he hoped Madeleine’s parents would soon be cleared of any involvement in their daughter’s disappearance. "Kate and Gerry have nothing to hide and we hope they will be cleared as soon as possible," he said.

Meanwhile, it emerged that police in Bosnia have failed to follow up an alleged sighting of missing Madeleine.

A British tourist believes he may have seen the missing girl while on a trip to the Roman Catholic shrine of Medjugorje in Bosnia on November 1.

The man, from Fermanagh in Northern Ireland, was said to have became suspicious after seeing a little blonde girl with a dark-haired couple, who he felt could not be her parents.

He heard the girl cry: “I want my Daddy" before a man clamped his hand over her month and “shoved" her into a car. The witness claims that he reported the incident to the local police but because of language difficulties was not able to make a full report.