The couple are suing Portuguese newspaper Tal & Qual for alleged defamation after it published a front page story claiming detectives believe the couple was responsible for Madeleine's death.

They say the article implied that the Policia Judiciaria (PJ) in the Algarve think the four-year-old died from an accidental overdose of drugs, possibly sedatives. The couple, from Rothley in Leicestershire, have grown increasingly angry about the speculation surrounding their daughter's disappearance. They have told friends they will fight the criminal case all the way to the courts. If successful, they can then apply for indemnity in the civil court.

If the McCanns do give evidence at trial, it will be the first time they have publicly discussed the case as they are not allowed to talk about the investigation.

But under Portuguese law, they can talk about events that night as part of other legal proceedings. "They are 100pc o­n this," said a friend.

"They will take it all the way if necessary and take to the witness stand to defend their reputations."

Yesterday, Mr McCann said the couple �?who are both doctors - were determined to challenge the "ludicrous" reports.

"Tal & Qual claimed we killed our lovely daughter Madeleine," he alleged.

"This is without evidence or truth. "The past 120 days have been horrific for us, our family and friends. We have tried to ignore some of the more ludicrous speculation but we simply could not ignore this report."

The cardiologist insisted he and his wife, both 39, were not suing for money and their lawyer Carlos Pinto de Abreu from Lisbon is working o­n a pro bono basis.

"Our daughter Madeleine was snatched from her bed o­n May 3," said Mr McCann. "She is still missing. The police have said time and time again we are not suspects.

"These are the facts. Everything else is at best speculation and in some cases downright lies."

Mr Pinto de Abreu said the couple had suffered enough without being the centre of press speculation.

"It is people's dignity which is being questioned, and it is their image which is being dragged through the dirt. What has been happening is not legitimate and, above all, is inhumane."

The legal action was prompted after Tal & Qual, a weekly newspaper with a circulation of 27,000, published a front page report o­n August 24 with the headline "PJ believes that the parents killed Maddie".