A libel trial will start today of a former senior Portuguese detective who published a book alleging that Madeleine McCann died inside her parents' apartment.
Kate and Gerry McCann launched legal action against Goncalo Amaral after he publicly questioned their accounts of what happened to their daughter.
The couple, both 41, from Rothley, Leicestershire, flew to Lisbon yesterday ahead of the three-day trial at the main civil court in the Portuguese capital.
Madeleine was nearly four when she went missing from her family's holiday apartment in Praia da Luz in the Algarve on May 3 2007 while her parents dined with friends nearby.
Four months after her disappearance, Portuguese police made Mr and Mrs McCann "arguidos", or formal suspects, in the case.
But their arguido status was lifted when the investigation was shelved in July 2008.
Mr Amaral at first led the inquiry into Madeleine's disappearance for Portugal's CID, the Policia Judiciaria (PJ).
But he was taken off the case in October 2007 after criticising the British police in a newspaper interview.
In his book Maddie: The Truth Of The Lie, published in July 2008, Mr Amaral claimed that Madeleine died in her family's holiday flat on the night she disappeared and questioned the McCanns' account that she was abducted.
A Portuguese judge granted an injunction in September last year banning further sale or publication of the book.
The former policeman was also prohibited from repeating his claims about Madeleine or her parents.
The McCanns travelled to Lisbon for the opening of the libel trial in December but the hearing was adjourned until this week after Mr Amaral's lawyer failed to turn up for health reasons.
The ex-detective's legal team is expected to argue that the material in his book is contained in the official Portuguese police files for the case, many of which were made public in August 2008.
Reports in Portugal suggested Mr Amaral plans to call a number of senior figures involved in the Madeleine investigation as witnesses.
They could include Jose Cunha de Magalhaes e Meneses, the local public prosecutor in the case, and Guilhermino Encarnacao, director of the PJ in the Algarve when the child vanished.
Mr Amaral's lawyers also sought evidence from a British policeman, Metropolitan Police Detective Sergeant Jose De Freitas, who was seconded to Leicestershire Police to help with the British end of the investigation.
But he is not expected to appear as a witness in the trial.
A Scotland Yard spokeswoman said: "We can confirm that the Metropolitan Police Service has received correspondence from the Portuguese authorities.
"This correspondence is currently being considered."
In a statement released through their Portuguese lawyers, the McCanns said their main motive for challenging Mr Amaral was to further the search for their daughter.
They also argued that Mr Amaral's book was "against the Portuguese constitution and against the Universal Declaration of Human Rights".
"All the court decisions we are trying to obtain are destined to prove Madeleine is alive and spread the information that her search is worthwhile," the couple said.
It is understood that Mr and Mrs McCann plan to attend all this week's hearings, but do not intend to return to Praia da Luz as they did in December.
The couple are also seeking 1.2 million euros (£1.08 million) in compensation for defamation in separate legal proceedings against Mr Amaral in Portugal.
They have said any damages awarded by the courts would go towards paying for private investigators to look for Madeleine.